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Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical crops and refineries. Fischer can additionally be 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 famous quotes was: “A man’s obtained to know his limitations.” This story illustrates why you should know your management valve’s limitations.
A consumer just lately known as for help downsizing burners on a thermal oxidizer. Changes within the manufacturing course of had resulted in an extreme quantity of heat from the prevailing burners. All makes an attempt to decrease temperatures had resulted in unstable flames, flameouts and shutdowns. The larger temperatures didn’t hurt the product but the burners have been guzzling a hundred and ten gallons of propane each hour. Given the high cost of propane at that plant, there have been, literally, tens of millions of incentives to preserve energy and cut back prices.
Figure 1. Operation of a cross connected air/gas ratio regulator supplying a nozzle combine burner system. The North American Combustion Practical Pointers e-book could be discovered online 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 challenge to retrofit smaller burners was being written. One of the plant’s engineers referred to as for a price estimate to vary burner controls. As we mentioned their efforts to scale back gasoline usage, we realized smaller burners may not be required to unravel the issue.
Oxidizer temperature is principally determined by the place of a “combustion air” management valve. Figure 1 shows how opening that valve will increase strain in the combustion air piping. Higher pressure forces extra air via the burners. An “impulse line” transmits the air pressure to 1 facet of a diaphragm within the “gas management valve” actuator. As air pressure on the diaphragm will increase, the diaphragm moves to open the valve.
The fuel valve is automatically “slaved” to the combustion air being equipped to the burner. Diaphragm spring tension is adjusted to deliver the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to maintain flame stability at considerably lower gasoline flows as a end result of there is a restricted range over which any given diaphragm spring actuator can present correct control of valve place. This usable control range is recognized as the “turndown ratio” of the valve.
In this case, the plant operators not needed to totally open the gas valve. They wanted finer resolution of valve position with much lower combustion air flows. The diaphragm actuator wanted to have the power to crack open after which control the valve utilizing significantly lower pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to allow recalibration of the gasoline valve actuator — utilizing the prevailing burners.
เพรสเชอร์เกจ would undoubtedly approve of this cost-effective change to the valve’s low-flow “limitations.” No capital challenge. No burner replacements. No vital downtime. Only a quantity of cheap elements and minor rewiring were required to save “a fistful of dollars.”
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