As companies dig deeper for new fuel sources, valve and bearing coatings can ensure long wear and fewer breakdowns
By Joe Zwers, Freelance Writer
The pursuit of non-conventional sources of oil and gas requires that valves, bearings and other components be able to withstand the highly abrasive materials they process. They must meet strict standards for use in offshore production, enhanced oil recovery EOR), molecular sieve, high integrity pressure protection systems (HIPPS), gas/oil separation process (GOSP) and other functions.
One way to improve longevity and reliability when dealing with erosive materials, such as during drilling operations or when extracting and transporting the sand-laden fuel from the Alberta, is to apply a hard, erosion-resistant coating to bearings, tees, manifolds and valve components. Several options for hardfacing these surfaces exist. Stellite, a group of cobalt-chromium alloys that may contain aluminum carbon, molybdenum, nickel, tungsten or elements, has been around for the better for the better part of a century. It has good wear and corrosion resistance properties, however, above 800 defrees Fahrenheit Stellite becomes soft and subject to heavy wear and tear, and galling of the valve seating surfaces.
Valv Technologies, therefore, developed a ceramic-metallic coating known as Ceramet, as well as a method of application known as the Rocket Applied Metallic (RAM) High Velocity Oxygen Fuel (HVOF) coating method. This involves using a rocket engine to generate a high velocity gas flow (Mach 3 – roughly 2,200 miles per hour) to coat the valve sealing surfaces with a super-hard chrome-carbide alloy. This process results in a 10-mil coating that has a rating of 70 on the Rockwell C-scale, several times harder than conventional coatings. At room temperature, RAM 31 has a Rockwell C hardness of 72, vs. 39.8 for Stellite 6. At 1400 degrees Fahrenheit, RAM has a Rockwell C hardness of 62, compared to just 8 for Stellite. RAM coated surfaces are also self-repairing in operation, opening the door to the achievement of over 1,000,000 valve cycles. The RAM coated surfaces are then diamond lapped for a precision fit. The hardness and temperature ratings to 1,800 degrees Fahrenheit combine to make these valves extremely resistant to attack by catalysts, abrasives and corrosive fluids. The surfaces are then diamond lapped to achieve a flawless seal.
Hardfacing versus Coating
But coatings may not be the only workable approach. More recently, a wear-resistant surface was designed by Valv Technologies for use in the most severely abrasive operating conditions. Unlike Stellite or RAM which coat the valve surfaces, Rhinoite is a hardfacing welding procedure that creates a matrix bond with the base material. The process creates a surface that is harder than any other coating or hardfacing and the Heat Affected Zone (HAZ) shows no signs of cracking. Another feature is that when there is any wear of the base metal, the Rockwell number actually rises since there is a higher ratio of tungsten carbide to weld matrix material.
Application is a two-stage process. In the first stage, the component is preheated and then the surface is overlaid with mild steel weld wire (duplex stainless steel, 309L stainless, carbon steel, Inconel, Colomony 56, tool steel or nickel alloys) together with tungsten carbide pellets.This layer is MIG welded to the base material. The second stage involves using MIG welding to overlay the first pass with weld material only, no carbide. During this second stage, a portion of the carbide pellets from the first overlay are dispersed into the weld puddle of the second overlay, producing a matrix between the weld metal and the carbide. This second pass normalizes the material from the first pass with the base material, causing the first pass material to become molecularly homogeneous with the base material and minimizing the HAZ. Microscopic examination of the material shows that a molecular reaction releases some of the tungsten from the pellets into the matrix material, forming a bond between the two. The surface can be up to 5/8″ thick with up to 80% of the material by weight being the tungsten carbide content.
The Houston Metallurgical Laboratory tested metal samples coated with Rhinoite. One test determined the hardness of the material at different depths and found a gradually increasing hardness as depth increased. At five mils (.005″) below the surface, the Rockwell hardness number (HRC) was 48, and ranged up to 62 as the measurements were taken throughout the outer layer. As the inner layer was hit at a depth of 250 mills (.250″) the hardness jumped into the 68-79 range. (See Hardness Profile Chart and Graph)
To test the corrosion resistance, another test was conducted for 2000 hours using direct spray salt fog (ASTM B117 – 90 – Standard Test Method of Salt Spray). A microscopic examination of the carbide coated surfaces showed little to no effect throughout the test period. At the end, when the overlay was removed, the component surfaces were virtually unaffected.
To test wear resistance, a 48,000 psi water jet with 250 g/min of 80 mesh fresh garnet was directed at a surface through a .040″ diamond orifice with a 1/8″ standoff and a 1/8″ per minute travers speed. The test produced a kerf with a depth of .025″ to .050″. This test result means that it would take as long to wear through ¼” of Rhinoite as it would to wear through 16″ of Inconel 718.
Out in the Field
Laboratory tests are fine, but what really matters is how the hardened surface performs out in the field. Over the last six years, Rhinoite has been used on elbows, t-sections and choke tubes in chemical plants and refineries with zero failures.
For example a Texas olefin plant uses it to extend the life of components of its steam cracking olefin furnace system. Over time, coke deposits form inside the furnace coils and these deposits need to be removed regularly to preserve plant safety and efficiency. The cleaning process involves shutting off the hydrocarbon feed and passing a 550°F steam/air mixture through the furnace to burn off some of the coke deposits, and crack off and blow away the rest. If the tubes are not routinely cleaned, the tube wall temperatures will rise causing the furnace to fail. However, the decoking process itself has risks. Sending 550° steam, laden with coke debris, through the tubes, at a speed greater than 60 ft/sec subject the components to severe erosion. In particular, the elbows, tees and pipe spools where the coke, air and water mixture exits the furnace into lines where the elbows, tees and pipe spools are subjected to an elevated degree of turbulence, velocity, and high-temperature carbonization. This causes the internal surfaces to erode and fracture, leading to costly repairs and unplanned shutdowns. Hardfacing on the internal surfaces of those components reduces the wear by a factor of five to seven times compared to bare metal, greatly extending their life and reducing plant maintenance costs.
Similar results are being obtained by resurfacing components used in the Canadian oil fields to reduce the erosion caused by sand in the oil and in other applications where components experience excessive wear.
For high-temperature (2200°F), highly erosive and highly corrosive applications, the Rhinoite process saves money by reducing shutdowns, equipment rentals, inspection frequency, manpower and replacement costs. And, if the hardfaced surface does eventually wear out, a new overlay can be added rather than having to replace the component.
New Biocontrol Approach Boosts Power Plant Production
By Carlos Elí Torres, PREPA and Eugenio Vives, NTS
In 2010, a cooling crisis at a Puerto Rico Electric Power Authority (PREPA) facility on the Island’s north coast near the capital of San Juan prompted operators to seek a greener solution to cooling tower biofouling via a mixed oxidant solution generated on-site from MIOX Corporation. The 590 MW Palo Seco Power Plant is one of the main suppliers of electricity on the Island, population 4 million.
Two years after the solution was installed, the MIOX on-site disinfectant generators have helped significantly improve water quality and energy efficiency at the power plant and resulted in dramatic savings in water, chemical and energy usage. The power plant increased its efficiency by about 40 MW within just a month of installing the new MIOX generators. Today, the cooling water is clean and free of hazardous chemicals; the generators are operating at the specified temperatures and the heat exchangers at optimal conditions; the compressors operate smoothly; and only one pump per tower is required to keep water running through the system.
Traditionally, the Palo Seco plant used a number of chemicals on its cooling tower water. With the new on-site generation technology, the only commodity delivered to the plant is food grade salt. The MIOX generators produce disinfectant when a solution of sodium chloride (NaCl) is passed through an electrolytic cell and electricity is added. This creates a dilute solution of 0.40 percent hypochlorite with traces of hydrogen peroxide and other reactive oxygen species. The particular system installed at the Palo Seco plant, the MIOX Dual oX Cell generates up to 30 pounds of free available chlorine (FAC) per day. This system is at the center of the new treatment regimen designed by MIOX’s exclusive local partner New Technology Systems (NTS) to increase heat transfer effectiveness and combat biofouling at the plant.
Alternative Biological Solutions
In May 2010, biofouling had gotten so bad it seemed as if a brown and green goo had invaded the cooling towers that would normally keep the equipment at the Palo Seco Power Plant operating efficiently at optimal temperatures amid the Caribbean tropical climate.
|Photo shows the fouled cooling system condensers, Photo courtesy of NTS.|
|Photo shows cleaned cooling system condensers after the system was treated with MIOX. Photo courtesy of NTS.|
Before, PREPA treated Palo Seco’s cooling water with conventional methods – a proprietary bromine and bleach based biocide from a local service provider to reduce algal growth, sulphuric acid for pH control, phosphonates for corrosion control and an antiscalant to prevent mineral deposits.
PREPA’s main issue was biological problems due to its close proximity to the San Juan Port as well as one the biggest Industrial Parks in Puerto Rico. As such, a lot of airborne particulates get sucked into the nearby cooling towers and offer an ample food source for algae and biofilm. The growth had reached a point that heat exchangers were plugged and temperatures rose in excess of manufacturer specifications due to limited ability of the biofouled cooling water to achieve effective heat transfer.
The biofilm at Palo Seco was described by one technician as “like mud growing in all the walls, all the pipes and all the valves. The water in the basin was slurried. We couldn’t see the bottom.”
PREPA called NTS, which had already been working with the utility on cooling water treatment at the Costa Sur Power Plant in Guayanilla on Puerto Rico’s southern coast.
NTS had been working with PREPA for four years at this point. A former engineering director in Puerto Rico’s high tech medical devices industry, I (Eugenio Vives) founded NTS in 2001 with Francisco Narvaez, PE.
|PVC Pipe in cooling tower basin before and after MIOX treatment.|
In partnership with MIOX for 10 years, NTS began working initially with the Puerto Rico Aqueduct and Sewer Authority (PRASA) on potable water projects. About five years ago, it got its foot in the door at PREPA with some pilot projects at smaller cooling towers at the 990 MW Costa Sur Power Plant in Guayanilla to test, refine and validate its treatment process for better control of biofouling, scaling and corrosion.
The Costa Sur Power Plant wanted to eliminate hazardous chemicals and improve the tower conditions. At that time, the equipment was experiencing issues caused by the deposits in the heat exchangers. The technology proved successful and two years after first installation, NTS was asked to provide a solution for some of the larger cooling towers at PREPA.
In Guayanilla, the MIOX results from the cooling towers at the two 80 MW smaller generators were similar to the two 400 MW larger ones – an immediate temperature drop and increased power generation load as biofouling was reduced. During the tests, NTS found that phosphonates used to control corrosion were acting as a food source for biofilm, particularly when disinfectant had to be cut prior to cooling tower blowdowns. As disinfectant was reduced in water to be discharged, the phosphonates prompted greater algae growth. With the previous treatment regimen, blowdowns occurred two or three times a week and was part of the reason for the severe biofouling. Instead of the phosphonates NTS added a complementary technology called “Hydrolator” which provides cathodic corrosion and deposits’ control. This unique biocidal approach developed by NTS combines a greener, more powerful disinfectant and anti-corrosion/scaling control solution.
Increasing Power Efficiency
While NTS was in the process of validating that particular technology, the company had an emergency at the Palo Seco Power Plant: there was trouble with high temperatures in the equipment due to serious biofouling in the system. One of NTS’s portable MIOX units was brought to the site and started treating the water with mixed oxidants solution. Results were seen immediately. The solution began to reduce the temperatures on the equipment and increased the energy load of the plant.
The efficiencies gained at the Palo Seco plant alone resulted in overall savings of roughly $34 million a year, said Pedro Polanco, chief chemist at PREPA. The success triggered the PREPA’s decision to install similar treatment systems on cooling towers at its San Juan Power Plant and to seek further expansion.
Such cost efficiency is doubly important, as 68 percent of PREPA’s power is generated from fuel oil, whose price volatility in recent years has prompted the utility to begin switching to natural gas as a fuel source. Palo Seco has four generating units – two at 85 MW and two at 210 MW. Due to biofouling, the generating units were operating close to 45°C – their limit – which had dropped the plant’s energy output to 80 MW and 195 MW when NTS was called. Within the first week of NTS’ solution, PREPA started seeing better results and, within the first month, the plant was operating under normal conditions well within its set point of 40°C and below.
|Cooling tower basin before and after MIOX treatment.|
Under the old treatment regimen, the hydrogen temperature in the PREPA generators was above 45°C with the valves fully open.
Everything was open and the heat exchangers were incapable of removing all the heat.
After installing the MIOX system, the temperature decreased, and all the generating capacity lost due to biofouling was gained back because the exchanger was cooling effectively.
It resulted in 40 MW of additional capacity in just one month.
Within four days of MIOX installation, NTS noticed that problems with generators, which had been operating at five or six grades over their temperature range, began to diminish.
“Before, bacteria count measured a tenth more than a million colony forming units per milliliter (CFU/ml),” said Rodrigo Rodriguez, NTS compliance technician.”Afterward, it fell to less than 100 CFU/ml, where it’s remained consistently. Likewise, the conductivity improved significantly, increasing from about three cycles to ten cycles and above.
“We continue to evaluate the critical process parameters such as bacterial growth, legionella, total dissolved solids, conductivity and others,” says Rodriguez.”The results are very impressive; overall the new bio-control approach works great.”
Reducing Operational Costs
The MIOX/NTS solution’s success also allowed PREPA to shut down one of the cooling tower’s two 400-horsepower pumps required to push water through the previously biofouled system – each of which uses about 4.8 million kilowatts per hour at a cost of $300,000 a year in energy consumption.
It eased operation and maintenance on the 10 to 12 compressors for the plant as well as the heat exchangers that were once being replaced as often as once a month.
When the heat exchangers would plug, the temperature would cause them to break. Prior to utilizing MIOX systems in their cooling towers, PREPA’s O&M costs were approximately $2.5 million and higher a year. After the system was running on all units, O&M costs fell to $1.1 million; nearly a 57 percent reduction.
In addition, the new bio-control approach allowed elimination of chemicals from the cooling water treatment regimen, which amounted to 31,000 pounds of chemicals stored on-site a year. That totals 31,000 pounds of chemicals not introduced to the plant or the local environment, in addition to savings for shipping, handling, storage, training and documentation for those chemicals.
In total, the introduction of the MIOX technology at the Palo Seco Power Plant allowed for a 56 percent reduction in water consumption – amounting to a savings of 40 million gallons per year. Uninhibited by biofilm and scaling deposits, the temperature drop increased by as much as 6-7°C. And the power plant load increased on average by a minimum of 10 percent, or 20 megawatts.
Chief chemist for PREPA, Pedro Polanco, who oversaw installation of the on-site mixed oxidant generator at both the Costa Sur and Palo Seco plants, said the power authority achieved the results it wanted by using MIOX.
“We wanted to prove that alternative chemical treatment would solve the problems we were experiencing in our cooling towers. We experienced good results with MIOX, and we will continue the treatment,” Polanco said.
The Palo Seco project was recognized during the 2012 Environmental Congress, sponsored by the Puerto Rico Manufacturers Association. Competing against numerous high tech industry competitors, PREPA and NTS won not only Innovative Project of the Year but recognition in two other categories: Water Conservation and Energy Conservation. Based on these results, NTS is currently using MIOX to treat 14 cooling tower units for PREPA, with more to come.
Eugenio Vives, BSEE/MBA, is the President of New Technology Systems, Inc., a Puerto Rico-based company focused on consulting services as well as sales and distribution of water treatment products. Mr. Vives has participated in the development of several patents for new industrial process and has earned NTS major awards from professional organizations such as the PR Manufacturing Association, the American Society of Quality Control and General Electric Co.
Carlos Elí Torres Veláquez is the Senior Chemist at Palo Seco Power Plant and has been working for 17 years in different positions in the Puerto Rico Electric Power Authority. He has been in charge of the SCR removal in the Cambalache Power Plant; the Condensate Polishers Evaluation and Optimization; Demineralizer Plant Evaluation and Optimization; and the Cooling Towers Evaluation and Optimization in the Palo Seco Power Plant.
Gas Turbine Remote Monitoring
By Dane Overfield, Software Product Development Lead, Exele Information Systems, Inc.
|Mitsubishi’s Remote Monitoring Center in Orlando, Fla.|
Continuous remote monitoring and historical trending for practically limitless operating parameters allow a major turbine OEM to formulate recommendations that assist their gas and steam turbine customers in making informed business maintenance and repair decisions. For gas turbines, consistent quality of planned and predictive maintenance over time is essential to achieving superior equipment availability, performance, and lifetime ownership cost.
Proactive and Responsive Monitoring
Mitsubishi Power Systems offers real-time monitoring and advanced prediction of potential problems through a 24-hour http://www.mpshq.com/service/gas_turbine_service/remote_monitoring.html“>Remote Monitoring Center (RMC) located in Orlando, FL.
All data points received from each unit are streamed into the RMC every one to three seconds, and stored for no less than two years for historical reference, making this system a very dynamic troubleshooting tool. Approximately 1,000 to 3,000 data points are monitored for each gas turbine configuration, including all of the auxiliary system information. Examples of parameters monitored for a standard gas turbine unit include:
- Ambient Conditions
- Hot Gas Path Conditions
- Combustor Dynamics (CPFM)
- Control System Features
- Vibration Indications
- Valve Demand, Position and Feedback Signals
- Auxiliary System Parameters
- Alarm Indications and Set Points
While most of their competitors will do a batch summary of the information once or twice per day, Mitsubishi receives continuous data stream of thousands of points of data per second in real time. All of this data comes back to their OSISoft PI System in the Orlando monitoring facility where they use Exele TopView Alarm Management Software to congregate the alarms from every monitored installation, globally. Exele TopView provides audible, visual and even email alarm message notification to the RMC Staff. Any unexpected deviations alert the RMC staff to take immediate action.
Alarm Management and Notification
About a year ago RMC looked to find an alarm management package that could serve their needs.”The alarm management package that we had been using for years was no longer supported by the manufacturer” said Daryl Massey, Manager of the Remote Monitoring Center.”In addition, we had outgrown the package as we continued to add to the number of monitoring points so we ran into more and more issues.” They choose Exele TopView Alarm Management and Notification Software.”TopView had a lot of benefits. It’s very flexible, it offers several notification options and the support has been great”, said Massey.
Exele TopView interfaces directly with the OSIsoft PI system and is currently monitoring 30,000 alarm tags and many more data tags. With so many potential alarms, one issue that the RMC Staff had to deal with is redundant or repeating alarms. These are situations where an alarm condition has been noted and corrective action is in the works, or where there is a defective sensor causing the alarm. So Massey and his technical staff requested that Exele Information Systems add a ‘Snooze’ feature to TopView which would allow the operator to disable an alarm for a period of time while corrective action is being implemented.”One of the best things about switching to TopView has been the ability to get updates and enhancements” said Massey.”We had spoken to Exele about the nuisance alarm situation and they explained the ‘Snooze’ approach and we had the feature available to us in a new release shortly after”.
Having the tools to successfully monitor abnormal gas turbine conditions, notify the appropriate personnel, and empower them to respond accordingly, can save a tremendous amount of time and money. Exele TopView’s breadth of features and ease of use provides a powerful and versatile solution that has been proven successful across many industries including multiple remote monitoring centers.
Boiler Replacement: Custom or Off the Shelf?
By Joe Zwers, Contributing Writer
Typically, there are two choices in selecting a boiler. One approach is to order a package boiler, fabricated in the factory and shipped to the site for installation. The alternative is to obtain a “stick-built” boiler which is built on site. Package boilers are the less expensive option, but they come in standard sizes and are not optimized for specific site conditions and requirements. Stick-built boilers are far more costly and take longer to install. On the plus side, they are designed for that particular application.
Alternatively, there is a hybrid which combines the best of both approaches. Each boiler is custom built to customer specifications, preassembled and tested. It can then be shipped to the site in one or more pieces for final installation and commissioning. Since they are factory built, they are less expensive and don’t require the extensive site work associated with stick built units.
Valero Energy Corporation needed to replace an aging 250,000 lb/hour boiler at its Memphis plant. It opted for a hybrid design.
“For the first boilers, we went through a bid process and selected Rentech based on both the economic and technical proposals they submitted,” said Walker Garrison, Technical Advisor for Utility Infrastructure at Valero, who serves as subject matter expert for water treatment, boilers and compressed air systems.
Valero followed this up with two more 250,000 lb/hr boilers for other plants and is now installing a 350,000 lb/hour boiler in Corpus Christi. Each is supplied by Rentech Boiler Systems, Inc., which favors the hybrid boiler approach.
The Corpus Christi boiler uses a non-traditional design. Typically the components, including the steam drum and boiler, are prefabricated in the shop and shipped to the site. But because of the large steam capacity of the Corpus Christi boiler, coupled with Valero’s interest in a conservative design, it is too large to ship in one piece and so a modular design was used. The furnace and convection section will be preassembled in the factory, but the steam drum is being shipped separately. A crew then came to the site to assemble the components, mounting the steam drum along with the risers and downcomers.
A total of four new Valero boilers have been designed to follow steam load, firing up and down with the demand, and typically produce 750 degree steam at 450 to 650 psi. But there are differences specific to the needs of each site. For example, the control systems vary from one location to the next. Generally the boilers are controlled separately though a distributed control system (DCS), with the plant management system distributing the load among the boilers. But the details vary from site to site, with some plants being more manual and others relying more on their control system.
The functions of the boilers are also different. Two of the units are designed as high turndown units that can run reliably at low fire and then ramp up when needed. Even though these new boilers are more efficient than the other units, since the older units can’t be turned down as reliably, the new boilers are kept at the minimum level until needed.
Garrison says that the boilers have operated well, reliably providing the required steam, avoiding unplanned shutdowns, and doing it in an efficient and environmentally friendly manner. It’s now four years since the first unit at Memphis went online. The others are more recent.
“The older boilers have about 85 percent to 87 percent lower heating value efficiency, but the newer ones have 91-92 percent efficiency,” Garrison said.”And, while we were EPA compliant before, these take us from an older emissions control technology to Best Available Control Technology (BACT).”
Custom vs. Off the Shelf
There are times when selecting predesigned, package boiler is the best option. If price is more important than reliability or efficiency, such as when there are multiple boilers on site with excess steam capacity, then it can make economic sense to purchase a lower cost boiler.
But when reliability, efficiency and low emissions are primary criteria, it is better to purchase a boiler custom designed and built for the exact needs of the site. This can include features such as larger furnaces to minimize problems with flames or air circulation and larger steam drums to provide greater more time to ride through short term feedwater issues. In non-attainment areas, lower emissions can be achieved by integrating the boiler, the SCR and low-NOx burners.
In such a case, having the boiler built and tested in the factory before shipping to site results in lower costs and shorter construction and commissioning times than having the unit built from scratch on site.
Mark Otteman, owner of Power System Sales and Service, a manufacturers’ representative specializing in boiler applications and pollution equipment, prefers the a cautions and conservative approach to boiler selection and operation, rather than dealing with firms specializing in small, hot rod boilers.
He provided an example:
If you allow water to carry over from the steam drum into the superheater, it will eventually blow out the superheater. Having a large steam drum allows better separation for getting water out of the steam before it goes to the superheater. In addition, if you lose feedwater flow to the boiler, the larger steam drum allows more time to correct the water issue before the steam levels drop.
“With some boilers you have a little over a minute from normal operating level on the steam drum to low level trip,” said Otteman.”If you have a problem with your feedwater there isn’t a lot of time to react to correct the problem. With Rentech boilers, you are sitting in that five minute interval, which gives someone a lot more time to react to a feedwater situation.”
This design concept minimizes the amount of refractory, so operators don’t need to worry about replacing refractory seals or rebuilding refractory walls. According to Otterman, the end result is improved reliability.
“The superheaters are buried back in the convection section, so they are protected from the temperature of the exhaust gas going into them,” said Otteman.”This helps extend their life.”