LETTERS

Problem unsolved

Your article ["Metal oxides at industry cusp," August 2004] regarding the analysis of stack gas for NO^sub x^ is very interesting but does not solve the problem. Removing sulfur from these gases is very important, and there are various methods for controlling it. Oxides of nitrogen present a more serious intractable problem. Important as it is to analyze the quantity of NO^sub x^, the control of that emission is both expensive and difficult. Processes for NO^sub x^ removal from the stack gases are both cumbersome and expensive. Removal of NO^sub x^ from stack gases is a highly desirable goal.

Nitrogen compounds are a very severe pollutant, and today there is no simple or inexpensive method for removal. Some years ago I learned about and bought some stock in a company called NOXSO. They had what seemed to be a very effective process for scrubbing nitrogen compounds from stack gases. For some reason the company eventually collapsed because they could not generate enough orders for their equipment. I have considered this a very unfortunate development.

It seems to me that you will find it worthwhile to investigate this and give it some publicity.

S. Ted Isaacs, P.E., Cincinnati, Ohio

Coal worth another look

Politicians say a great deal about freeing us from dependence on foreign crude oil imports. Their ideas are generally based on conservation or, alternatively, on opening crude oil deposits in sensitive environments. Nothing is said about the use of alternative hydrocarbon resources.

The Black Hills of South Dakota and Wyoming got that name because of the mountains of coal just under the surface. It is one of our vast sources of hydrocarbon that lies virtually untouched.

I served as one of the lead engineers for instrumentation in the design of SASOLII, the second of three mine-mouth coal gasification installations in South Africa. When completed, the three plants made that country independent of foreign oil.

I recently completed a period as manager of instrumentation engineering in the design of a 200-ton-per-hour coal liquefaction plant to be built in Manchuria. This will provide the crude oil equivalent feedstock for a large petroleum refinery to be built on the site. The process will be copied to eventually make China independent of foreign oil.

At one time it was said that coal-to-oil plants resulted in higher costs for the crude oil equivalent. These cost figures require review against today's conditions.

A number of pilot plants using various coal-to-oil techniques are in operation in this country, and have proved the feasibility of the conversion. A more modern study of costs and ROI could result in the construction of a number of full-size facilities. Eventually we would be free of the Saudis.

Karl Spindler, Control Systems Engineer, Lower Gwynedd, Pa.

Software sees nonlinear

I would like to clarify the article "Temperature sensors" [Control Fundamentals department, August 2004] concerning thermistor temperature sensors. The generalization of the devices as being accurate only over narrow spans applies only if you are referencing a linear output. The resistance-temperature curve is indeed very nonlinear for NTC [negative temperature coefficient] devices; however, the repeatability along this curve is very consistent. With the proliferation of digital instruments, the difficulty of interpreting the nonlinear response has been addressed by software. Thermistors are toleranced as pointmatched (±°C) at a given temperature set point, or curve tracking (±°C) over a temperature range. When used within the standard thermistor temperature range of-65°C to 200°C, an interchangeable accuracy of ±0.2°C over a 100°C range is common, with ±0.1°C also available. When point-matched, an interchangeable accuracy of ±0.05°C or better can be readily accomplished.

Jay Kochaver, Quality Thermistor, Inc., Boise, Idaho

Offshoring cuts into tax base

One more late comment on Ellen Fusscll's "Offshoring-New hope for U.S. or inevitable as death?" in your April 2004 issue. There is a broader issue here that goes beyond one company's interests. It has to do with providing a tax base to support the infrastructure that every business-and every individual-depends on. You can't offshore schools, firemen and policemen, road maintenance, bridge repairs, or the countless things that the tax base makes possible.

My standard of living does not depend solely on my wages; it also depends on the number of folks helping bear the cost of our shared infrastructure. The growth of offshoring not only increases the polarization between rich and poor, it also degrades the overall condition of life in the U.S. I'm not a fan of big government, but when market pressures drive business behaviors that are detrimental to the entire country, I believe that government has a legitimate role in controlling those behaviors. It is time for limits.

Bob Queenan, Idaho Falls, Idaho

Q&A URL

Your interesting articles in the CCST [Certified Control Systems Technician] department oilnTcch magazine update and refresh me in various aspects of instrumentation. However, these questions are scattered, and I would like to compile and preserve them for future reference. Could you please supply a resource?