By Jeff Elliott, Technical Writer
Steel piping systems are widely used at coal-fired power plants for a variety of purposes, including the conveyance of coal ash slurry to nearby settling ponds, the transfer of limestone slurry to absorber spray towers for removal of sulfur dioxide (SO2) and hydrogen chloride (HCl) from flue gases and for transporting away the calcium sulfate by-product of the flue gas desulfurization process.
However, when these abrasive, caustic slurries are transported through steel pipe, the effect on the inner surface can be devastating. Abrasive wear within these transportation systems is produced when hard particles are forced against or slide along the wall of the pipe. The loss of material is the result of the hard, sharp angular edges producing a cutting or shearing action on the pipe wall, which in more extreme cases can result in pipe leaks and even failure, or significant maintenance costs and downtime for pipe replacement.
For these abrasive applications, mild steel pipe is not tough enough to stand up to the abuse for more than a year or two. As a result, maintenance engineers are seeking superior piping alternatives to reduce maintenance and prolong system life, at a price point that will not significantly impact the budget.
“The slurry is so abrasive, that standard grade carbon steel pipe just wears out too quickly,” said John Pillard, a senior pipe technician with experience in high abrasion applications.
One-hundred-twenty-nine-million tons of coal ash—a byproduct of the coal burning process—is produced in the U.S. every year. Most power plants transport the coal ash in liquid form to large surface impoundments or in solid form at landfills near the facility through long lengths of steel piping, which can range in length from several thousand feet to miles. There are almost 900 such landfills and surface impoundments in the U.S. today.
Limestone slurry is also commonly used by coal-fired plants for the effective removal of sulfur dioxide and hydrogen chloride from flue gases. These wet scrubber flue gas desulfurization (FGD) systems utilizes a pumped in limestone slurry through which flue gas containing SO2 is passed in absorber spray towers. The limestone slurry reacts with the flue gas, removing the SO2. The limestone in slurry is then converted into calcium sulfate. This waste material produced by the process is then pumped out from the bottom of the spray towers through steel pipe for further treatment for use in commercially viable by-products such as gypsum board and cement.
To deal with the extremely abrasive and caustic nature of these various slurries, plant maintenance managers are looking to a variety of “abrasion resistant” steel pipe products and accessories to replace standard mild steel pipe in these high wear areas.
Most abrasion resistant pipe options operate on the premise that when two objects meet, the harder object wins. As such, products are available in a variety of increasing hardness, measured on the Brinell Scale from A-R steel (200 BHN) through iron cast pipe (up to 800 BHN).
Unfortunately, any product that is very hard throughout the wall thickness is also brittle. This brittleness is unacceptable as piping systems are constantly flexing and moving as a result of pressure surges and spikes and due to mechanical and physical contact at the facility.
However, one type of pipe delivers the best of both worlds: an induction hardened pipe with an abrasion resistant inner surface that tapers to a strong, yet ductile outer surface.
Manufactured by Port Washington, Wisc.-based Ultra Tech, this pipe is produced under the Ultra 600 brand. Ultra Tech begins with a steel pipe manufactured to a proprietary chemistry, followed by induction heating and finally water-quenching the inner surface to create a single-wall pipe.
At 600 BHN, the inner surface of this induction hardened pipe can withstand most common abrasives and tapers to a 250 BHN outer surface that is ductile enough to accommodate normal handling during shipment, installation and maintenance. With this process, pipe can be created in various diameters up to 40”, in varying lengths and wall thickness.
Because the outer surface behaves like mild steel, the product can be cut and welded with proper procedure in the field, configured into a variety of fittings and can accept the standard end options of flanges, weld rings and couplings. The company can also produce the pipe in long-radius bends to further reduce wear and eliminate the frequent replacement, repair, and associated expense accepted as the norm at the bends and elbows in high wear applications.
Pillard estimated that in an extremely high wear area an A-R pipe could wear out in as little as a year and a half. He estimated the Ultra 600 could double that duration in the same location. In a lower (yet still abrasive) wear application, Pillard has seen the induction hardened pipe last 6 to 8 years.
Author: Jeff Elliott is a Torrance, Calif.-based technical writer. He has researched and written about industrial technologies and issues for the past 15 years.
Simple Cycle Turbine Emissions Control by Improved AIG Distribution
By Peter Reinke, Utility Assistant Superintendent and Dr. Richard Martin and Christopher Ferguson, Callidus Technologies by Honeywell
This article pertains to a GE LM6000 operated in simple cycle mode at a site in New York. The turbine and selective catalytic reduction (SCR) system were commissioned in 2004. The plant is permitted to operate on natural gas with 2.5 ppmvd (corrected to 15 percent O2) limits on NOX and 10.0 ppmvd (corrected to 15 percent O2) limits on ammonia slip. Prior to implementing the subject ammonia injection grid (AIG) improvements, power output of the plant was limited by SCR performance and plant operators were injecting high levels of NOX water in conjunction with operating the “Sprint Water” system to maximize power while operating within permitted emission limits.
Representatives from Callidus Technologies by Honeywell met with plant superintendants and proposed a project to evaluate and potentially improve SCR performance. Prior to communicating with Callidus Technologies by Honeywell, the plant superintendant had commissioned a third party “SCR system evaluation.” The “SCR system evaluation” cited catalyst plugging, ammonia misdistribution and gas bypass around the catalyst as the primary causes of performance loss at the utility and recommended an emission traverse test. The emission traverse test found ammonia maldistribution as the primary cause of non-performance of the SCR system and suggested that the maldistribution was due to a combination of unbalanced flow through the ammonia injection grid (AIG) and insufficient flow through the ammonia vaporization box. The flow rate through the ammonia vaporization box was approximately half of the designed flow rate.
Proper AIG performance requires mixing a relatively small ammonia gas stream with the much larger turbine exhaust flow. Callidus Technologies pioneered the use of computational fluid dynamics (CFD) modeling of combustion processes and has over 20 years experience in related designs of burner systems used in combined cycle applications which require a similar uniform mixing of small amount of fuel into the turbine exhaust.
Callidus Technologies ran comparative CFD models of the AIG and ultimately proposed a low-cost bolt-on retrofit for the existing AIG. After installing the bolt on retrofit, plant operators saw an immediate improvement, which enabled the plant to increase megawatt output by 7 percent while maintaining SCR emissions within permitted limits. Plant operators now have the option to generate an additional 3.3 MW of power while operating within emissions limits and not forced to enable the “Sprint Water” system. NOX water is the controlling factor, while maintaining NOX at 2.4 and ammonia slip at 7.5.
Since the plant’s initial commissioning, operators had struggled with achieving power output in conjunction with acceptable emission levels. To generate above 38 MW the operator had to use the “Sprint Water” system to maintain mandated compliance.
The operator had to try to operate within 1/100th of ppm to keep the average emissions below permitted limits. Operating at these levels required continuous tweaking of turbine parameters to maintain power output while maintaining average emissions. The demands placed on the operators to maintain SCR emissions took precedence over other plant functions.
The SCR catalyst had been tested in the last three months and the report indicated sufficient catalyst activity. Based on emission traverse test data and the “SCR system evaluation” report the utility decided to focus on the catalyst plugging, gas bypass, vaporization box flow and the ammonia injection grid distribution. Regarding the gas bypass, the utility sealed gaps along the inside walls of the SCR and replaced the catalyst seals. To address catalyst plugging, the NOX blocks were all removed and each block was hand vacuumed. A considerable amount of insulation was found between each block during this cleaning process. A gas diverter was designed and fabricated to improve flow through the vaporization box. The plant superintendent also called in Callidus Technologies to assist in the flow distribution problem. Callidus Technologies visited the plant to collect operating data as well as physical data for the existing ammonia injection grid.
Based on traverse test data and the SCR system evaluation report the team decided to focus on the ammonia injection grid (AIG). Visual inspection of the system confirmed that distribution of the ammonia into the turbine exhaust gas was most likely a major contributor to the lack of control of emissions. The existing grid consisted of a number of small pipes with small holes drilled in the pipes that introduced the ammonia flow into the turbine exhaust gas. The small-diameter holes and low ammonia flow rates do not provide sufficient penetration or mixing of the small ammonia stream into the large stream of turbine exhaust gas.
Because performance of the ammonia injection grid is a major factor in achieving maximum SCR performance, Callidus developed a proprietary grid design for use in their SCR systems. The Callidus design borrows from their experience in burner mixing technology and incorporates a discharge port arrangement and low pressure loss flow “turbulators” to achieve a high degree of mixing of the ammonia and turbine exhaust gas in a short distance downstream of the ammonia injection grid. The following comparative CFD analysis provides an indication of the improved mixing achieved by the Callidus design when compared to a conventional ammonia injection grid design.
Two illustrations from a CFD analysis depict the degree of mixing of the ammonia plus carrier gas with the turbine exhaust gas for conventional “drilled pipe” ammonia injection grid designs. Figure 1 shows the ammonia plus carrier gas concentration at 1 foot and 3 feet downstream of the ammonia injection grid. Also shown is the variation in concentration along the center plane of the duct. Figure 2 provides the location of the points at 3 feet downstream of the injection grid that were used to compute the RMS deviation of the ammonia plus carrier gas concentration. The RMS deviation at 3 feet is 97.6 percent.
|Figure 1 Basline Typical “Drilled Pipe” AIG Ammonia Plus Carrier Gas Concentrations|
|Figure 2 Three foot RMS 97.6 percent|
Figures 3 and 4 from a second CFD analysis depict the degree of mixing of the ammonia plus carrier gas with the turbine exhaust gas for the Callidus proprietary grid design. Ammonia plus carrier gas concentration at 1 foot and 3 feet downstream of the ammonia injection grid are shown in Figure 3. Also shown is the variation in concentration along the center plane of the duct. Figure 4 provides the location of the points at 3 feet downstream of the injection grid that were used to compute the RMS deviation of the ammonia plus carrier gas concentration. The RMS deviation at 3 feet is 5.2 percent. This high level of mixing improvement is achieved with less than 0.21 inches water
|Figure 3 Callidus Design Ammonia Plus Carrier Gas Concentrations|
|Figure 4 Three foot RMS 5.2 percent|
It was decided to use certain features of the Callidus design to improve the ammonia distribution at the subject plant. Callidus Technologies focused its efforts on analyzing the existing ammonia grid to determine the existing ammonia plus carrier gas distribution as well as evaluating the effectiveness of certain features of the proprietary design to improve the mixing. One of the main design considerations was to improve mixing without introducing significant increased pressure drop. The CFD team had additional constraints in that their scope did not include changes to turbine flow upstream of the ammonia injection grid. Consequently, from a modeling standpoint the CFD team adopted a comparative case methodology which held turbine flow constant while evaluating various ammonia injection grid modifications. Using this comparative approach, the CFD team evaluated a variety of geometries and configurations which provided improvements in both mixing and flow with minimal pressure drop. These various configurations were also evaluated for ease of manufacturing and more importantly ease of retrofitting.
Based on the CFD modeling the final “bolt-on” field modification design improved the RMS deviation of ammonia plus carrier gas at 9 ft downstream of the ammonia injection grid from 132.2 percent to 16.9 percent with an additional total pressure loss of less than 0.1 inches water column. This improvement was achieved without the use of all of the Callidus features because of retro-fit constraints.
Based on the CFD analysis, Callidus Technologies designed and manufactured a field retrofit kit for the existing ammonia grid. The kit was comprised of 108 baffle plates which could be carried through the man doors of the SCR and bolted to the existing AIG. The plant maintenance team installed the retrofit kit during a scheduled outage. The total installation was completed in less than four man days. The unit was brought back on line and the performance improvement was immediately apparent. With minimal operator tuning the plant exceeded all prior power levels while maintaining emissions. Plant operating data and plant emission data were collected and analyzed to provide comparative measures of operation before and after the AIG improvements were implemented. Four months of data was analyzed. The first two months of data captured 22 turbine runs for a total of 76.8 operating hours before the AIG improvements. The remaining two months of data captured 23 turbine runs for a total of 96.2 operating hours. Each turbine run was analyzed to provide an average operating metric for megawatts, NOX, and ammonia slip. A plot of the average operating metrics for all of the runs both before and after the AIG modifications can be seen in Figure 5.
Figure 6 compares the average of all runs before and after the AIG improvements. The average MW increased by 7.7 percent, the average NOX decreased by 0.7 percent and the average ammonia slip decreased by 11.6 percent.
The performance change was immediately apparent the moment the unit was first fired after the upgrade. Within hours of operating with the upgrade the plant emissions were holding within permit limits without the need of excess NOX water and generating higher output without using the Sprint system. Additionally the operators were no longer tied to making constant adjustments to meet emissions, and were able to allocate their time to other plant operations. Perhaps most importantly, the performance improvements were achieved at lower capital cost as compared to other third party recommendations to re-engineer or replace the entire ammonia injection grid.
Significant plant performance improvements were achieved through the combination and application of key technical disciplines combined with real world plant experience. Experience in other industrial fluid mixing applications resulted in a patent pending AIG design which out performs traditional “drilled pipe” designs. Portions of this high performance AIG design were then proposed as a means to improve mixing performance of the existing AIG. CFD modeling was used to validate the retrofit design and indicated a potential to improve ammonia distribution which in turn would improve SCR operation. Design for field installation resulted in a bolt-on kit which was easily installed with minimal down time. Qualitative interviews with plant operations indicated that the AIG modifications resulted in immediate positive results. Quantitative analysis of plant operating conditions indicate significant improvements in power output with additional reduction of ammonia slip while maintaining NOX within permit levels. These results were achieved with reduced capital cost and equipment downtime as compared with other recommendations. It is possible that similar methods can be utilized to improve performance at other facilities.
Authors: Pete Reinke is assistant superintendent of power plants and has 20 years of experience. Dr. Richard Martin is combustion technologies specialist with 40 years of experience in combustion systems design. He is founder of Callidus Technologies. Christopher Ferguson is involved with Honeywell’s aBusiness Development Catalyst Group.
Is Lime Souring Your Valve Operation?
By Todd Loudin, President, Larox Flowsys
Lime is used by a large majority of the process industry in either a powder or liquid form. Engineering and maintenance personnel often face a long and potentially expensive trial-and-error period in order to find the best process equipment to handle lime.
Limestone is mined from a quarry in the form of calcium carbonate (CaCO3). Then it is crushed and fed into a kiln at approximately 2,000 F, where the carbon dioxide is burned off (calcining) to make calcium oxide (CaO). CaO is ground into a powder in a tower mill, a spiral classifier, or a slaker. The milk of the ground lime is used for many industrial purposes including pH control, power flue-gas cleansing, calcium extraction in pharmaceutical manufacturing, and more. One of the most common uses of lime in the chemical process industry is pH control.
Lime is extremely difficult to handle in piping systems, instrumentation and valves because its particles are very jagged and will not dissolve, but rather merely suspended in solution. Any cracks or crevices will cause the lime particles to fall out of suspension and fill these voids. Lime further aggravates this situation when it hardens in these collection points. The lime changes its state to a solid mass of material—commonly referred to as scaling. Scaling causes a pipeline’s inner diameter to become smaller and smaller. Material buildup on valve seats and other surfaces can cause the valves to freeze in position.
Process equipment, instrumentation and valves selected for use in lime slurry systems should limit cavities, cracks and void areas. Even a small collection point of lime can cause equipment failure and countless hours of downtime and maintenance.
The ideal product to supplement lime slurry should be able to clean itself and break apart scale. It should also be completely free of void spaces, cracks and cavities. A piping product installed in a lime slurry system should be full port in order to limit obstruction and potential lime slurry buildup.
A significantly oversized actuator is a typical initiative for increasing plug and ball valve performance in lime slurry systems. Because the size of the actuator is increased, the output capability is roughly two times the normal manufacturer’s recommended torque for clean liquids.
An oversized actuator may improve performance while decreasing downtime as a result of sticking valves, but it will not solve all related maintenance problems. Because lime is very abrasive, it affects most ball and plug valves severely. A hard material cover such as stellite coating on the ball will help protect the valve against the abrasive nature of lime.
The seats also are a major concern. Again, hardened-steel seats with a scraping edge are most likely the best alternative in lime applications. “Scraping” hard-coated metals will perform better in scaling substances because they have the ability to scrape built-up material off the ball and plug surfaces.
Most polymeric seats will not maintain durability over time in lime slurry. The scaling that occurs in these valves is like a wrecking ball to most polymeric seats. The ball or plug with scale buildup is turned through these seats, usually resulting in a short lifetime. Because ball and plug valves have cavity areas that house the ball or plug, a substantial amount of material accumulates in this void area over time. It is beneficial to install flushing ports in the valve so that the body cavity area can be cleansed water to wipe out material accumulation after each cycle. This process will help minimize material buildup in the cavity area.
It is expensive to build a ball or plug valve with the all of the previously mentioned features. The cost of a ball or plug valve equipped with these features can be five to six times the price of a traditional Teflon-seated ball or plug valve. Unfortunately, however, the performance of most Teflon-seated ball or plug valves in lime slurry is less that satisfactory.
Gate and knife gate valves can be used in many slurry services. Most gate valves force the gate into a wedge area to close the valve, so tight shutoff is not always guaranteed.
Knife gate valves have a sharpened edge to improve the ability to cut through solid particles. In lime service, the seating area is a spot for material accumulation. The lime will accumulate in this area, causing difficulties in valve operation, which could prevent sealing the valve completely against the line pressure.
The ideal knife gate valve for lime service features a hard-surfaced leading knife edge. Actuator forces in knife gates should be increased to give the valve the ability to cut through or close tightly against the lime buildup in the wedge.
The knife of the knife gate is exposed to scaling and the scale buildup on the knife is most likely accumulated from packing problems in knife gates. As the knife opens, the scale buildup is dragged through the packing, which requires increased forces to open the valve. In most instances, there significant packing leaks occur.
Utilizing knife gates in lime slurry service requires a scraping packing material. This material should be a hardened substance that has the ability to scrape the knife clean with every operation. The knife gate valve should have increased actuator forces that are capable of dragging the knife through the packing material.
Pinch valves are an efficient solution for lime slurry service because they have a straight-through design with no crevices or cavities for material collection. Pinch valves have a proficient self-cleaning effect on scaling materials.
A rubber tube or sleeve is pinched by steel bars on the centerline of the valve, causing it to close. Upon stretching the rubber sleeve, it begins to reach the closing position and the material or scale buildup flakes. As the valve is being closed, the flaking becomes greater, but the fluid velocity increases substantially. Thus, the flaked material or scale is pressure washed from the elastic surface of the rubber sleeve.
Pinch valves also address abrasion concerns. When dealing with abrasive flows, there are two options. The first is to make the ball, plug, or gate valve and piping materials much more hard and durable. The second approach is to make the valve or piping material softer. Softer materials allow the abrasive particles to bounce off the surface without destroying it.
For this reason, pinch valves have been used in mining applications on very coarse slurries for the past 30 years. With any mineral-based slurry, pinch valves are a very viable option for protecting against abrasion. A pinch valve also offers protection against clogging or jamming that can occur with other valves in lime slurry service. Many valves such as ball valves with stellite or harder coatings may be able to withstand the abrasiveness of lime slurry. However, they are subject to jamming or clogging because they have cavities that allow for material collection.
Pinch valve selection must be performed very carefully and with due diligence. Stainless steel or carbon steel ball valves and plug valves do not vary greatly from one reputable manufacturer to another. Choosing one of the “more reputable” ball or plug valves, will most likely guarantee a valve free from porosity or imperfections. In addition, some ball or plug valves have modified designs to enhance performance in difficult services.
Pinch valves, however, can vary greatly from one another, and rubber quality and properties can differ drastically from one manufacturer to another. A comparable analogy is purchasing automobile tires with the option of either a 30,000-mile set of tires or an 80,000-mile set. Side by side, these tires look almost identical, but the 80,000-mile-rated tire certainly will cost more. The price increase secures two times the useful life of an inferior tire.
If you have tried them in the past and have been unhappy with product performance, then perhaps the make you selected was simply “inferior.” You might wish to give pinch valves another try with a different make and manufacturer. Good designs are available, and reputable companies will stand behind their products after the initial sale. A high-quality pinch valve typically handles lime slurries without any special product enhancements.
A pinch valve or diaphragm that has a preset weir could decrease valve performance quite substantially, however. This nonflexible weir will accumulate scale; because it does not flex, it will result in increased wear to the rubber sleeve. The nonflexible weir also defeats the self-cleaning effects of pinch valves.
Many manufacturers and valve users try to force their standard valves into applications in which they do not belong. Obviously, a large process plant tries to standardize products as much as possible in order to cut costs with spare parts and personnel training.
However, what many large plants fail to recognize is that this practice may in turn prove to be very costly. I recall a situation where a company was using a standardized control valve that needed repairing every six months. However, when they finally switched to a product that was more suited for a slurry process, the plant was able to double its mean time between failures.
The plant had 22 control valves in this process. The five-year operating cost of the previously used 22 control valves, excluding the cost of downtime, was $242,000. By replacing these valves with better-suited slurry control valves, the five-year cost was reduced to $55,000.
The financial ramifications of improper valve, instrumentation, and piping selection for processes such as lime slurry can have a long-term negative impact on most operations. Although a simple lime slurry control loop for pH control in many chemical plants is a very small portion of the process, it can be a large drain on operating costs. Plant decision-makers would be wise to choose process valves and instrumentation for this portion of the process carefully.
Chemical process plants can select from a wide array of valves for use in lime slurry service. I did not exclude any types of valves intentionally. I attempted to focus on the types of valves more commonly used in lime slurry, as well as to offer recommendations that might help improve valve performance, regardless of which type of valve is selected. Improper valve selection for lime slurry service can have a significant negative effect on continued operating costs. A larger up-front investment could result in quite substantial savings in the future.
Are You Ready for RICE NESHAP?
By Jay Warner and Chad Kaderabek, Universal Acoustic & Emission Technologies
Although most government regulations are looked upon as impediments, the RICE NESHAP (Reciprocating Internal Combustion Engine, National Emission Standards Hazardous Air Pollutants) ruling from the Environmental Protection Agency can be looked upon as a business opportunity to some.
The ruling, issued in February 2010, covers existing non-emergency stationary diesel engines. Compliance takes effect May 3, 2013. EPA states there are over 900,000 stationary engines in the U.S. that are affected by this ruling.
Revenue opportunities caused by the ruling will include new engine sales, catalyst sales and labor for installation of catalysts. Engine distributors and packagers particularly have an opportunity to generate revenue from this ruling for the following reasons:
- They already have a database of previously sold packages
- They have existing relationships with end-users as they provide them service and/or replacement parts.
- Their customers will be looking for answers to the question: What do I need to do to my engine to be compliant by 2013?
- Customers with non-compliant engines may opt to purchase a new compliant engine instead of retrofitting.
Now is the time for a packager to be looking for a solution to this opportunity. Some items they need to consider are:
- Type of control technology
- Backpressure requirements
- Catalyst placement
- Supportive structure
- Catalyst sizing
- Catalyst configuration
- Compliance testing
- Continuous monitoring
- Labor time
Emission control technology that will be used is Diesel Oxidation Catalysts. One needs to be aware of the type of coating on the catalyst element’s substrate. Platinum coated substrates are more durable than Palladium. Platinum lasts longer and is more robust to poisons like sulfur. RICE NESHAP requires CO reduction by 70 percent. Most catalysts on the market today are calibrated on the order of 90 percent CO reduction and therefore would be more expensive. Look for a catalyst provider that can adapt to these lower CO reduction requirements.
Engine backpressure also needs to be considered when adding a catalyst to an existing engine. Adding a catalyst will add backpressure that may exceed the engine exhaust backpressure threshold. A catalyst can add an additional 3 to 4 inches of water to engine backpressure. Replacing the silencer with a combination silencer/catalyst unit is a solution to minimize the additional backpressure. They are designed for lower backpressure by reducing the number of expansion and contractions of the exhaust gases.
Another option is the catalyst itself can be designed for lower backpressure. Placement of the catalyst in the exhaust system is critical as the exhaust gas temperature needs to be managed so the catalyst works properly. Most catalysts need to operate above 250 C. The further the gas path is from the source, the lower the temperature. In some applications, this may require additional insulation around the exhaust system in order to maintain the proper exhaust temperature. The system should be optimized for the lowest temperature seen throughout the year.
For example, colder climates may need additional insulation because of winter temperatures. Also, proper attention needs to be paid to the components upstream from the catalyst system. If you are using a packed silencer in sequence with the catalyst system, fibers may come loose that may coat or plug the catalysts element and reduce its effectiveness. In these instances, the catalyst system should be located upstream from the packed silencer.
Before installing the catalyst system, the physical support structure needs to be considered. For larger catalyst systems, the connecting pipe will not be able to support the catalyst’s weight. A steel ladder system may be required to support the catalyst from the package’s base. The supportive structures should be fabricated before on-site installation to minimize service time.
Proper attention needs to be given to catalyst sizing. The volume of the catalyst most be properly sized for the exhaust flow rate to meet the required emissions reduction target. If it is undersized, you won’t meet the emissions target. And if it is oversized, the catalyst may be overpriced and uncompetitive when selling to an end user.
Catalysts require periodic servicing, typically every 8,700 hours of operation. The catalyst system needs to be placed where it can be easily accessed, whether near a service panel or open area. Engines less than 500 HP may utilize a more economical disposable/non-service catalysts housing. For larger HP Engine applications, it is more cost effective to utilize a removable catalyst element housing design. This design should allow easy access and removal to the catalyst element without special tools or cumbersome capture mechanisms. The quicker to remove and replace the catalyst element, the more time your technicians have for other billable jobs.
Exhaust bypass is a common problem in some catalyst housing designs. This is where the exhaust gas circumvents the element and is not forced through the catalyst. This issue will impact the effectiveness of the catalyst system. Seek a housing and catalyst design that includes a positive seal against the side of the housing, forcing the exhaust gas to flow through the catalyst element.
Many engines that will be affected by the RICE NESHAP ruling will come in enclosed skid-mounted packages. Space inside the enclosures is at a premium. Finding a location to fit a catalyst can be difficult. However, by using an integrated silencer/catalyst system, you may be able to place it in the same footprint as the current silencer. Also, you will need catalyst housings that have different mounting configurations, such as end-in/end-out, side-in/end-out, and high-side in/end-out.
Existing stationary engines that require the addition of a catalyst system require before and after emissions testing to validate compliance. To make this requirement easier for your organization, work with an emissions control supplier who can provide the testing. In this way, the emission control supplier can receive information immediately if changes need to be made to meet compliance.
An additional opportunity for your organization is continuous monitoring requirements. The RICE NESHAP ruling requires engines that are larger than 500 hp and are a major source of hazardous air pollutants to maintain a service log of catalyst differential pressure and temperature. You can sell and install a continuous monitoring system to make this documentation requirement easier for your customer. Offer a continuous monitoring device that allows the storage of multiple readings. Also, a monitoring device with CANBUS capabilities will allow integration into a facilities Building Automation System. Or, you may want to consider offering a monitoring service to your customers that will handle the data tracking requirements for a monthly or yearly fee.
Labor time to retrofit an existing stationary engine is quite variable. One needs to consider the catalyst systems size, weight, site accessibility, lifting equipment, if the package is enclosed or open and installation complexity. Because compliance requirements aren’t until 2013, you have time to actively seek some test project sites to hone the skills and techniques required before the majority of the retrofit projects take place.
Anatomy of a Three-Component Composite Compliant Repair
By Osmay Oharriz, Chemical Engineer, Belzona Inc.
Composite repairs have been gaining greater acceptance among asset owners and equipment operators not only because these repairs provide an engineered, durable and affordable solution but also because they comply with international engineering standards.
Three-component composite repair systems are typically composed of paste grade material, resin and reinforcement sheet. As the composite repair system must form a bond with the substrate to be repaired, it relies upon the adhesive quality of the base material or resin for its strength. Paste grade epoxies can be used as base materials based upon their adhesion, mechanical properties and erosion-corrosion resistance when compared to other nonmetallic systems such as polyurethane, methacrylate, alkyd, vinyl and polyester-based polymers and resins.
A resin film is applied to the reinforcing sheet to eliminate wicking/capillary failure modes along the fiber strands of the reinforcing sheet. The reinforcement sheet will provide strength to the repair and hoop strength where required. They are usually made out of carbon or glass fibers. Carbon fiber sheets are more costly, more rigid, and difficult to cut, design, and apply, in comparison with glass fiber. Glass fiber is less rigid, often increasing the long term cycling performance for such a solution.
As mentioned, the growth in acceptance and usage of composite repair systems is inherently related to the availability of standardizing documentation. Two of these standards, ASME PCC-2 and ISO /TS 24817.
ASME PCC-2 “Repair of Pressure Equipment and Piping”: Article 4.1 of this standard provides the requirements for the repair of pipework and pipelines using a qualified nonmetallic repair system. It defines repair systems as those fabricated of a thermoset resin used in conjunction with glass or carbon fiber reinforcement among other allowed materials. Likewise, it provides guidance in assessing defects stemming from external corrosion involving structural integrity damage or not, internal corrosion and leaks. Furthermore, it covers all the methodology to follow for designing such repair systems, along with some other design considerations such as external loads, cycling loading, fire performance, electrical conductivity, cathodic disbondment and environmental compatibility.
ISO/TS 24817 “Petroleum, petrochemical and natural gas industries-composite repairs for pipework-qualification and design, installation, testing and inspection”: This Standard displays all the requirements and recommendations for the qualification as well as for the design, installation, testing and inspection for the external application of composite repairs to pipework suffering from corrosion or other source of damage, most commonly presented in the oil and gas industry. This standard defines composite repair laminates as those with carbon, glass, polyester or any other similar sort of reinforcement material in a polyester, vinyl ester, epoxy or polyurethane matrix. The standard also provides mathematical guidance in assessing external and internal corrosion problems with or without structure integrity damage.
While both standards give extensive information and guidance on how to design, apply, test and inspect composite repairs systems, ISO/TS 24817 Standard allows for the application of repairs onto more complex geometries such as damaged clamped surfaces, bends, T-shaped piping, reducers, flanges and cylindrical vessels among others. It also considers the repair expected lifetime in the design equations.
Compliant composite repairs differ from other traditional noncompliant repair systems. Not only do compliant composite repairs rely on a pre-qualified material and pre-defined mathematical design but also on competent application craftsmanship. That is why all personnel in charge of the execution, inspection and design of such repairs shall be properly trained and validated by the composite repair manufacturer. The validation process is addressed to train and certify installers, supervisors and designers of composite repair systems.
Potential installers and supervisors undertake off-job training and initial validation in a training environment, where they will receive theoretical and practical instructions in the installation and supervision of composite repair systems. Installers complete a test piece repair that is then inspected and destructively tested to ascertain quantitative data on that application performance. In addition, supervisors attain full validation on a live application project after a prudent time agreed upon by the composite repair system manufacturer.
At least one repair system manufacturer also requires that potential designers undertake training and validation in a training environment where they will receive theoretical instructions on the design methodology for each defect type and geometry. Designers will be assessed by the composite repair system manufacturer. Installers, supervisors and designers are issued a certificate and identification card by the composite repair system manufacturer.
Once the damage is assessed by the end user or client, he or she should contact the composite repair supplier. The supplier is often the validated application company who contacts an approved design company who will in turn submit a design data sheet to the client. This report is intended to collect all the information pertaining to such damage and potential repair and shall be completed by the client. A good communication between the client and the designer is paramount in fully understanding the nature of the problem and possible repair.
Some of the data to be supplied by the end user and gathered by the designer includes, but is not limited to the following.
Original equipment design variables consisting of process design conditions, mechanical loads and a detailed description of the damaged area. Any complementary information such as isometric drawings, pictures or schematics is deemed necessary.
Maintenance and operational history including documentation of any significant changes in service conditions, past repairs and any inspection reports detailing the nature of the area to be repaired.
Service condition data including expected repair life time, required design and operating variables, expected future service conditions and required time scale for the application.
End user service detailing all the facilities to be provided by the end user should the repair be approved.
This information collected on the design data sheet is used by the designer to initially confirm the type of repair based upon the nature of the defect and the geometry of the repair.
Composite repairs can be designed for type A and B defects. Type A defects are those within the substrate, not through-wall and not expected to become through-wall within the lifetime of the repair system (see Photo 1). This type of repair is considered to be relatively easy as it only requires structural reinforcement.
|Type A defect on a straight pipe section|
Type B defects, on the other hand, do compromise the structural integrity of the system and require through-wall sealing as well as reinforcement (see Photo 2). This is why they are considered to be more complex repairs. The geometry of the repair can range from a straight pipe section, bend, tee, flange, reducer, to a cylindrical vessel. The level of complexity in the repair will increase in the same order.
|Type B defect on a straight pipe section|
Once the type of defect and geometry of the repair are confirmed, the designer will calculate the repair parameters which are thickness of the composite repair, axial extent of the repair, and number of required wraps. The designer will contact the end user to formally authorize or reject the composite repair application. If the application is authorized, the repair parameters should be shared with the end user. The installer will be carrying out the application and, as explained earlier, will possess proper validation issued by the composite repair manufacturer.
Prior to the application, the surface to be repaired will be prepared as per NACE No. 2/SSPC-SP 10 “Near White Metal” and freed from contaminants as per SSPC-SP 1. Surface angular profile shall be at least 3 mills (75 micron) confirmed by Testex Replica Tape QA QC measurements as per NACE RP0287.
Application should commence as soon as the surface preparation activity has been completed. The first layer of paste grade material is important as it levels the substrate to be repaired, which is liable to be uneven or pitted due to external corrosion. Without this paste grade material, the reinforcement sheet would be much less likely to achieve an optimum bond with the substrate. This is why the paste grade material should be pushed deep into the substrate profile in order to minimize the risk of air entrapment.
The reinforcement sheet should then be wetted with the resin and wrapped over the first layer of paste maintaining a pre-fixed degree of overlapping thorough the axial extent of the repair. In order to achieve intimate contact between layers, firm hand-pressure should be exerted in every wrap. The angle at which the reinforcement sheet is laid should be alternated in every wrap to make the fabric fibers as multidirectional as possible, hence ensuring that the repair is strong in all directions.
The same procedure should be repeated until the required number of wraps and composite repair thickness have been achieved. The final layer should be of paste grade material to ensure that the last reinforcement sheet wrapped around the repaired surface is completely covered and is therefore protected from mechanical damage. Photo 3 depicts a three-component composite repair after completion.
|Three-component composite repair after completion|
Three-component composite repair systems allow the asset owner and/or equipment operators to restore weakened and/or damaged substrates by means of an engineered and compliant solution. These systems are designed to extend the lifetime of piping systems and substitute temporary repairs. Personnel responsible for the design and execution of composite repairs shall be trained by the composite repair system manufacturer and certified against international standards ASME PCC-2 and ISO/TS 24817. Good communication among all personnel involved in the composite repair process is fundamental in bringing the repair to fruition. Composite repairs are indeed the right solution for extending the lifetime of equipment in an efficient and reliable manner.
Author: Osmay Oharriz, Chemical Engineer, has been working at Belzona Inc. for two years. He is responsible for the Oil & Gas Industry and is an integral part of Belzona’s engineering team.
Capital Project Management Systems
By Paul Verveniotis, P.E., Vice President Industry Solutions, Skire
Every public power utility strives to provide the best customer service possible: reasonable rates, limited outages and quick field repair response times. But sometimes this already complex task seems overwhelming given the challenges facing electric utilities these days. Our nation’s power grid is more than 50 years old—far exceeding its life expectancy. It cannot support demand from a rapidly expanding population and integrate a variety of new, renewable energy sources while operating on a deteriorating infrastructure. As a result, power is expensive and unstable. The American Society of Civil Engineers rated our grid a shameful D+.
Power utilities can do better, and many are. Technology is paving the way to an updated, reliable power grid of the future. One company looking to use cutting-edge technology to remain at the forefront is DTE Energy, a diversified energy company involved in the development and management of energy-related businesses and services nationwide. DTE Energy is one of the nation’s largest energy suppliers, serving more than three million customers in Michigan. The company’s major projects group has a capital program encompassing a portfolio of nuclear, coal, natural gas and renewable energy projects.
Leading power utilities recognize that a core commitment to customers and stakeholders is good stewardship by spending and investing their money wisely and providing reliable, efficient and environmentally sound energy. They have recognized the importance of building and maintaining state-of-the-art infrastructure.
To meet customer commitments, utilities realize the need to look for ways to improve across all areas of the business that are critical to achieving their business objectives, including how they manage capital projects. Executives have identified that capital project management systems can further enhance an organization’s ability to keep these projects on track, on time and on budget; and improve their ability to meet financial and performance goals.
A capital project management system has many compelling features: it standardizes workflows, approval and reporting processes; aggregates data to make it searchable and accessible; includes configurable security standards; offers an intuitive interface; is easily configured; and facilitates real-time collaboration with its service providers throughout the project lifecycle. Most importantly, though, industry leaders look for a solution that will take existing siloed data and bring it together, creating a live, interactive environment in contrast to the existing disconnected environment created by multiple sources of project information.
Bringing Data to Life
Many power utilities still manage capital projects the old way: passing around hard copies, saving documents to desktops, and managing project costs and schedules in spreadsheets. It is becoming clear that the old methodology of relying on multiple disparate tools for project information is inadequate and too inefficient for managing large capital investments. Leading companies now recognize that these practices could lead to disorganized projects, misplaced or obsolete data, no collaboration, and wasted time and money. With such a large number of people relying on them for power, these utilities have recognized the benefit of leveraging technology to mitigate these risks and sought to implement a comprehensive capital project management solution that would standardize processes and reduce operating costs, while supporting the company’s strategic initiative for continuous improvement.
DTE Energy selected Skire Unifier as its companywide project management information system (PMIS). A PMIS can provide a single source of truth for project data and project management business processes to ensure consistency, automate approvals, facilitate collaboration, and ensure all project stakeholders are working with the most up-to-date data possible. Skire’s Unifier PMIS can provide a broad set of features and benefits when deployed across a capital project portfolio:
- Business Process Automation—Critical business process, such as change orders, RFIs, design reviews, invoices and permits, may currently be captured, tracked and routed manually for review and approval. With Unifier PMIS, construction processes can be submitted electronically and automatically sent through a pre-defined workflow to make certain all relevant parties review and approve each item. By standardizing and streamlining these project management processes, ensuring all project related information is being reviewed by the appropriate individuals and storing the information in a centralized system, construction groups look to achieve a significant cost savings across a capital program.
- Auditing & Reporting—PMIS offers features that can significantly reduce the time and effort required to generate project reports and auditing information. Standard reports can be set up to run automatically, and ad-hoc reporting is simplified since the information is in a centralized location. All activities are recorded dynamically in the system to help meet regulatory auditing requirements and further reduce project risks.
- Collaboration—The Unifier PMIS provides a mechanism for real-time collaboration both internally as well as with its services providers throughout the project lifecycle. All project team members can have access to the latest project information to ensure that updates and changes are communicated immediately, so that everyone is working with the latest project drawings, documents and data.
DTE Energy also strives to move up the Project Management Institute’s Project Management Maturity Model—a model that helps organizations benchmark their project management practices and identify areas that need improvement. The implementation of Skire Unifier can help organizations ensure that they are delivering on their commitment by automating standardized processes and providing tools that support continuous process improvement. With Unifier, DTE Energy has identified these goals:
- Integrate a variety of systems, including SAP, so that critical information is available in real time,
- Standardize work processes to ensure the correct information is gathered and stored at the accurate time,
- Improve overall project controls, including cost, schedule, scope and resources,
- Better collaborate with contractors and business partners, and
- Optimize processes to increase efficiency.
Powering the Future
The concept of harnessing renewable energy isn’t simply a trend; it’s a must if utilities want to meet the increasing demand for power and consumers’ desire for renewable sources of energy. Organizations that don’t feel the need to commit to environmental responsibility will be left behind, while others rise to the top. In fact, Detroit Edison currently funnels 500,000 MWh of renewable energy through its power grid.
Michigan has lofty renewable energy goals and meeting them will require significant investment in its energy infrastructure. Michigan Governor Jennifer Granholm is establishing Michigan as a leader in the renewable energy game, both in harvesting it and powering the state with it. She has stated that Michigan will reduce its dependency on fossil fuels by 45 percent by 2020. In order to help meet the needs of the state, DTE Energy is focused on being able to bring renewable energy to the grid—whether that be wind, solar, hydroelectric or biomass—quickly and efficiently. Implementing a PMIS is an important step in helping Michigan meet its renewable energy goals.
A comprehensive PMIS can help ensure that new renewable energy installation projects are kept on track by enabling the project team to work smarter and more efficiently by using a disciplined, fact-based approach. Consolidating all project information into a single centralized and integrated system helps to streamline the project delivery process. Project stakeholders will be able to keep track of construction processes; have greater control over budget and spending; and have insight into multiple projects in one system. This will become increasingly important following the passage of the Clean, Renewable and Efficiency Energy Act (PA 295) that was passed into law in October of 2008 encouraging the development of renewable energy projects in Michigan. Under the approved plan, Detroit Edison plans to substantially increase investments in renewable energy through 2029, focusing on the following:
- 550-600 MW of utility-scale wind farms. If the turbines are 2 MW each, this would mean building about 280 turbines.
- 20 MW of solar energy through the SolarCurrents program.
- 600 MW of renewable energy from third parties in Michigan.
Large power utilities serve millions of customers who rely on them to deliver power quickly, efficiently, and with minimal interruptions to service. Recognizing the need to invest in both new and existing infrastructure projects, the implementation of a comprehensive PMIS can represent a major step in support of their project execution goals. A comprehensive PMIS can not only help deliver projects more quickly, but it can also assist in the stewardship of constituent and government funding during the planning and construction phases by helping to manage projects more efficiently.
Solar Inversion Station Addresses Energy Cost per Watt
By John Skibinski, Vice President Renewable Energies Market Development, American Electric Technologies Inc.
Utility decision makers evaluate solar energy against the same standards as other sources of energy production. How can solar energy cost per watt over a 20-year depreciation cycle be driven down while maintaining a fixed price per watt on a power production sales contract, yielding favorable return on investment (ROI)? There are a number of ways to lower solar power cost per watt in this scenario. It can be accomplished at functional points in the system resulting in system end-to end-efficiency; at functional points in the system resulting in system end-to-end reliability; through initial equipment and installation cost savings and through maintenance costs savings across the total operations life cycle.
|ISIS grid tie inverter control unit. Courtesy: AETI|
Ultimately, a key objective for pursuing solar energy production is to sell solar power at a profitable margin over a capital equipment life. Depreciation has been one method for meeting this objective. In addition, the emergence of various renewable energy credits has enabled solar power generation to become a more viable form of power production. Solar tends to be favored more than other renewable energies and is advancing towards grid parity energy costs fastest because it has few moving parts, and is easily piloted and scaled upward after piloting into megawatts, making it more cost effective to implement, maintain and scale up over time.
Along with much advancement, the industry has faced numerous challenges, foremost among them being reliability and efficiency. For the past two decades, the solar industry has seen some improvement in efficiency, reliability, initial equipment and installation costs and life cycle operations and maintenance costs at functional points in the system, such as solar cell degradation and power distribution component life.
However, the industry has not addressed improving cost per watt end-to-end as part of total system design. Also, inverters still tend to fail after five to seven years. One reason is low to the ground air intake with high volume air intake using low-cost filters which are easily clogged by dirt and dust, resulting in overheating the inverter and depowering it. Second, foam and paper filters are easily chewed through by rodents and insects that compromise the cables inside. This particular issue has been such a problem that solar system integrators have adopting the practice of mounting stainless steel mesh screens over air intakes and exhausts to address this vulnerability.
Today’s solar farms are designed by searching through catalogs and stringing the functions together, bundling boxes at the construction site with little optimization by design, manufacture or construction installation; a total departure from the way utilities design power plants. Sometimes the boxes are then mounted into a shipping container requiring the use of a large air conditioner that is metered by its own incoming power while the outgoing solar power is metered separately; another expensive approach that does not reflect utility power plant design.
For years, efficiency in transmission lines has been improved by increasing end-to-end voltage, yet the same is true for designing with higher photovoltaic (PV) voltages across the farm. Many 1,000 volt PV solar panels are tested beyond that. So, it makes sense to move solar field PV string voltages up to the 1,000 to 1,100 volt range, among the highest levels possible for today’s solar inverter power modules. When using higher efficiency thin film PV panels, this means that 10 to 20 percent more PV power can be captured through the inverter. For a high-efficiency thin film PV string of 2.5 amps, 250 to 500 watts of additional power is now possible per PV string, yielding 100 to 200 kW more per 1 MW farm field. This enables utility-scale solar farms to produce 50 to 100 MW more per 500 MW farm field. This provides solar power for more customers per year and lowering cost per watt while generating additional solar energy revenue.
American Electric Technologies Inc. has designed a utility-scale integrated solar inversion station (ISIS) to address the solar industry’s need to cost-effectively and reliably increase the number of watts captured per PV string. By taking the utility’s view of power plant design and construction, ISIS integrates the functions of 1,100 volt, 1,600 amp master combiner, arc-less DC/AC disconnect, liquid cooled dual 500 kW grid tie inverters, 12.47 kV or 13.8 kV step up transformer with all fuses, surge suppressors, lightning arrestors, protection and interconnection relays, communications networking and IEEE 1547 system pre-commissioning.
Using ISIS, the EPC wires the PV input cables and MV output cables as AETI completes commissioning. The end result is one integrated non-containerized NEMA 3R PV direct to 13.8 kV solar inversion station fully revenue ready after wiring.
The station’s liquid and air cooling system allows operation in sunny climates during high temperatures while delivering output power with no-derating or separately powered air conditioner. Liquid cooling provides heat transfer and keeps power modules cooler at a constant temperature, which lengthens power semiconductor life. In addition, liquid cooling pumps last longer than high-velocity air cooling fans or blowers. With low cost radiator technology as a heat exchanger, liquid cooling allows an inverter to operate beyond 50 C ambient temperature without de-powering.
ISIS also uses utility-grade temperature reactive components and hardened programmable controllers designed and tested for greater reliability, yet features flexible integration with utility SCADA systems. ISIS integrates all functions of solar inversion into one platform, reducing costs and minimizing system downtime. Dual redundant solar power inversion paths address the industry concern about the life of one single 1 MW inverter. The use of dual redundant 500 kW power inversion paths improve long-term reliability by ensuring at least one of the systems is operating at all times.
By achieving lower costs over the life of capital equipment while increasing watts produced, utilities receive a greater return on solar power generation that could result in solar power becoming the first of the renewable energies to reach grid parity energy costs by 2016 without incentives. Eventually, all utilities will be examining ways to improve renewable energies power generation ROI end-to-end across the project without incentives. The introduction of AETI’s ISIS will help the industry reap those rewards by capturing the highest possible production and cost savings rates now available.
Circular Vibratory Screeners for Ash Processing
By Henry Alamzad, President, Kason Corp.
The JEA Northside Generating Station had two expensive crushers approaching the end of their service lives. JEA knew that replacing the aging crushers, a necessary component in the ash-processing system, would entail major capital costs. The crushers performed the essential service of preventing bed-ash particles larger than 3/16 in. (7.6 cm) from entering the disposal process, since oversize particles would plug the pumps that move the ash slurry to a settling basin. The company wanted to find a way around the cost and operational limitations of the crushers while still ensuring that oversized particles were separated.
Circular vibratory screeners scalp oversize particle that could otherwise plug pumps.
The benefits JEA targeted were ambitious: (1) avoid the estimated $250,000 expenditure to replace two 30 in. (76.2 cm) diameter, double-roll crushers; (2) eliminate disruptive installation of these large pieces of equipment and associated labor expenses; and (3) reduce future maintenance requirements, which typically incurred downtime of a half-day or more. A new approach would enable JEA to improve the coal- and petroleum-coke-fired station’s ability to keep its baseload-power operation running with almost no shutdown for crusher-related maintenance.
The Northside Generating Station operates two of the largest circulating fluidized bed (CFBs) combustors in the world, each capable of producing nearly 300 MW and generating 2,000 tons of ash daily, 60 percent bed ash and 40 percent fly ash. During the time JEA was exploring alternatives to the processing of bed ash using double-roller crushers, it was also testing a circular vibratory screener for processing fly ash. JEA wanted to replace a 2 sq ft (0.185 sq m) shaker screen, which required constant maintenance, with a circular vibratory screener and reduce maintenance requirements. While seeking this replacement screener in the fly-ash line, it occurred to Jerry Kowalski, a structural engineer at JEA, that a circular vibratory screener might also be a good candidate for separating oversized particles in the bed-ash line, thus eliminating the crushers.
“Although fly ash is typically as fine and light as talcum powder, moisture in the circulating gas stream of the boiler can cause ash particles to form clumps larger than 3/16 in. (7.6 cm),” said Kowalski. “For this reason, oversized particles must be screened from the fly ash.”
Bed ash, which is coarse, heavy and resembles beach sand, exits the boilers as glowing grains close to 500 F (260 C) and is carried away from the boilers via a 100 ft (30 m) drag-chain conveyor. The conveyor deposits the bed ash into a 600 ft (183 m) long pneumatic line that transports it to a dedicated bed-ash silo, where the ash arrives cooled to approximately 250 F (130 C). After the ash cools to about 150 F (66 C), it is put through the crusher, then drops by gravity 8 ft (2.4 m) directly into a mix tank below. The fly ash enters the mix tank the same way. Both the bed ash and fly ash are mixed into a slurry made up of “on-size” particles in a single tank, then pumped 4,000 ft (1,219 m) to settling ponds. There is one bed-ash and one fly-ash silo for each of the two combustors, totaling four silos.
“Since oversize particles comprised less than 1 percent of our bed ash, the use of crushers was overkill, leading us to consider circular vibratory screening for scalping of bed ash in addition to fly ash,” said Kowalski.
Working with Kason technical representative Bernie Petrone of Southern Process Equipment Co., Kowalski installed two 48 in. (1,219 mm) diameter Flo-Thru Vibroscreen screeners, high-flow-rate units fabricated from epoxy-coated carbon steel and equipped with a single vibrating screen deck. Kowalski concluded that given the small percentage of “overs” in the bed ash, a single screen would suffice. The same two screeners were installed in the fly-ash line.
Each screener uses two, externally mounted, imbalanced-weight gyratory motors which provide multi-plane inertial vibration that causes on-size particles to pass through apertures in the screen while oversize particles travel across the screen surface in controlled pathways to a discharge spout at the periphery. On-size material passes through the screen at a rate of 50 lb/min (23 kg/min) to the bottom outlet directly below the inlet into the mix tank below. With the bottom outlet located directly below the top inlet, material falls vertically through the screen at high rates, permitting the screeners to keep up with the volumes of bed and fly ash the JEA plant processes daily.
Today, the two bed-ash and fly-ash lines are equipped with four high flow rate circular screeners replacing the square shaker screens and crushers. The circular screeners have enabled JEA to meet its goal of reducing maintenance on the bed-ash line and reducing screener maintenance by virtue of their epoxy-coated, stainless-steel, corrosion-resistant construction.
“The 48 in. (1219 mm) diameter screeners met the criteria we needed to rationalize switching technologies,” Kowalski said. First, the circular screener is about one-tenth the cost of a double-roll crusher. The new unit was small, which meant that JEA could install it easily and have it up and running quickly. Moreover, the small footprint of the unit would open up the work area and provide easier access for personnel and greater freedom of movement when maintenance needs to be done. “There has been no maintenance requirement in the months since these units were installed, but when any maintenance is required it can be accomplished in minutes instead of hours,” Kowalski said. All personnel have to do is remove the single screen and insert a replacement. Rapid maintenance is important, because JEA runs the screeners 24/7.
Kowalski said the new screeners allow removal of oversized material continuously. The “overs” build up in a special tank and at one to two week intervals are transferred by truck from the tank to a settling pond.
“The use of circular screeners instead of crushers has proven successful for us,” Kowalski said, “and they are performing well in both our fly- and bed-ash processing areas.”
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