Roll on, Columbia…
In the article “Hydroelectricity: The Versatile Renewable” (June 2009) the statement is made “…Grand Coulee Dam on the Columbia River in Washington State can go from low load to full load (about 800 MW) in matter of seconds.” This is the capability of just one of three Canadian General Electric generators in Grand Coulee’s Third Powerhouse. There are three other large Westinghouse generators in the Third Powerhouse. Their output is about 12 percent less than the CGE generators. In addition, there are two other powerhouses with 18 generators with outputs of about 125 MW when completely upgraded. In the pump generator plant there is another 300 MW of generating capacity. I believe the peak load is 6,600 MW.
I find it very refreshing that hydro power is now being referred to as a renewable resource. The environmental lobby has pushed to prevent that designation because of fish mitigation and similar issues with dams.
Coulee Dam, Wash.
Natural gas also rises
On page 44 of the article on hydrogen cooling (“Hydrogen Cools Well, but Safety is Crucial,” Power Engineering, June 2009) Nancy Spring wrote, “Luckily, when hydrogen does leak, it’s so light that it dissipates quickly, unlike natural gas, for instance, which is heavy and will sink to the floor and stay there.”
You were right about hydrogen being safe because it dissipates so quickly, but you were wrong about natural gas. Natural gas, also known as methane, is also lighter than air; density is 0.554 compared to air at 1.0. Methane will also rise and dissipate quickly. This is why natural gas vehicles are so much safer than gasoline-powered vehicles.
Because the word “gas” is used to describe gasoline, natural gas, LPG and propane, the public has a hard time differentiating between these very different chemical fuels. Correcting the confusion created by the ubiquitous use of “gas” is one of the more frustrating barriers to the widespread commercial deployment of these cleaner, safer, more efficient, less expensive and domestically produced motor fuels.
David E. Bruderly, PE
Clean Power Engineering/Wise Gas Inc.
Good electrical insulator
While I enjoyed your article on the application and safety issues with hydrogen cooling of generators, the first paragraph contains an omission. Hydrogen’s low density and excellent thermal conductivity are important in this application, but without a good dielectric constant these properties would be useless. In most generator designs, there are components that are electrically insulated only by the space between them, which is filled with hydrogen. Thus, being a good electrical insulator is at least as important as the other properties cited.
James B. Lewis, PE, Executive Engineer, Power Generation,
As a staff member of a commercial PEM fuel cell manufacturer and an alternative energy systems engineer for 19 years, I am very interested in the public’s perception of gaseous hydrogen.
In “Hydrogen Cools Well, but Safety is Crucial,” a figure is given on the equivalent TNT content of a standard 2,400 psi hydrogen cylinder. Though I found the article to be accurate and the cautions are all prudent, some perspective is also necessary to place the relative threat in context. Specifically, the TNT equivalent is one that is certainly quite alarming until placed into context with, say, a backyard propane tank for a barbecue.
This is not to diminish the care that should be taken with hydrogen. In certain environments that are not designed with sufficient ventilation, it is certainly possible to accumulate an explosive mixture. Yet, as indicated in the article, in many installations, hydrogen’s tendency to dissipate aloft is a more benign characteristic than that of propane (or other hydrocarbons) to sink, pool and accumulate in low areas. In our experience over the last seven years with fuel cells, it is actually quite difficult to accumulate hydrogen because it dissipates so quickly.
Mark Cohen, IEEE member
A not-as-sexy shift
One way to reduce the CO2 emissions without building a large number of new plants or developing sequestering technology is to shift our base load electrical production from coal units to the combined cycle units. A 500 MW combined cycle unit operating off of natural gas at 50+ percent efficiency will produce dramatically less CO2 than a similar sized coal unit operating at between 35 to 40 percent efficiency both due to reduced Btu’s and due to fuel mix. Currently many of the combined cycle units are either on cyclic duty or idled during parts of the year when electrical demand is down. The problems are electrical cost of production and converting the coal units to cyclic duty.
Electrical cost of production is a simple formula based on the plant operational costs and fuel costs. Conversion of the coal plants to cyclic duty is more complicated, but sliding pressure operation, insertion of division valves between superheaters, better pumps, valves and controls can go a long way to convert the base load units into more nimble (or at least not as lumbering) cyclic duty. Simple black and white (or green) values can be calculated, where people can be readily aware of the cost of reducing the CO2 production.
Switching production is a far smaller capital investment and quicker to implement than building hundreds of square miles of wind farms or solar power. It is definitely not as sexy and the costs are too easy to identify. Therefore in our current political climate, it is not likely to be done. Instead, it will be hidden behind cap and trade rules and bureaucracy.
Principal Engineer, Control Components Inc.
The article “New Couplings on Scrubbers” in the June 2009 issue incorrectly stated the capacity of First Energy’s W.H. Sammis plant. The correct capacity is 2,456 MW.
The article “Changing IX Resin Cut Acid/Caustic Needs” in the April 2009 issue omitted the name Purolite Co. as the company providing the solution to the demineralization performance problem described at Puerto Rico Electric Power Authority’s Aguirre plant.