Fischer: Know your valve’s limitations 

Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical crops and refineries. Fischer is also a part-time faculty professor. He is the principal reliability consultant for Fischer Technical Services. He may be reached at bobfischer@fischertechnical.com.
One of Dirty Harry’s well-known quotes was: “A man’s got to know his limitations.” This story illustrates why you have to know your management valve’s limitations.
A shopper lately referred to as for help downsizing burners on a thermal oxidizer. Changes within the manufacturing course of had resulted in an excessive amount of heat from the prevailing burners. All attempts to decrease temperatures had ended in unstable flames, flameouts and shutdowns. The larger temperatures didn’t harm the product however the burners were guzzling 110 gallons of propane every hour. Given the excessive price of propane at that plant, there were, literally, tens of millions of incentives to conserve energy and reduce costs.
Figure 1. Operation of a cross connected air/gas ratio regulator supplying a nozzle combine burner system. The North American Combustion Practical Pointers book can be found on-line at https://online.flippingbook.com/view/852569. Fives North American Combustion, Inc. 4455 East 71st Street, Cleveland, OH 44015. Image courtesy of Fives North American Combustion, Inc.
A capital project to retrofit smaller burners was being written. One of the plant’s engineers referred to as for a worth estimate to change burner controls. As we discussed their efforts to reduce back fuel usage, we realized smaller burners might not be required to solve the issue.
Oxidizer temperature is mainly decided by the place of a “combustion air” management valve. Figure 1 reveals how opening that valve will increase strain within the combustion air piping. Higher stress forces extra air via the burners. An “impulse line” transmits the air pressure to one facet of a diaphragm in the “gas control valve” actuator. As air pressure on the diaphragm increases, the diaphragm strikes to open the valve.
เกจ์แรงดัน is automatically “slaved” to the combustion air being equipped to the burner. Diaphragm spring tension is adjusted to ship the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to keep up flame stability at considerably lower gas flows as a result of there’s a limited vary over which any given diaphragm spring actuator can provide accurate control of valve position. This usable control range is called the “turndown ratio” of the valve.
In this case, the plant operators not needed to totally open the fuel valve. They needed finer resolution of valve place with much lower combustion air flows. The diaphragm actuator needed to have the ability to crack open after which management the valve using significantly lower pressures being delivered by the impulse line. Fortunately, altering the spring was all that was required to permit recalibration of the gasoline valve actuator — using the existing burners.
Dirty Harry would positively approve of this cost-effective change to the valve’s low-flow “limitations.” No capital venture. No burner replacements. No important downtime. Only a number of inexpensive components and minor rewiring had been required to save “a fistful of dollars.”
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