Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical crops and refineries. Fischer can be a part-time faculty professor. He is the principal reliability advisor for Fischer Technical Services. He could also be reached at bobfischer@fischertechnical.com.
One of Dirty Harry’s famous quotes was: “A man’s got to know his limitations.” This story illustrates why you should know your management valve’s limitations.
A shopper recently called for help downsizing burners on a thermal oxidizer. Changes within the manufacturing course of had resulted in too much heat from the present burners. All makes an attempt to decrease temperatures had resulted in unstable flames, flameouts and shutdowns. The larger temperatures didn’t harm the product but the burners have been guzzling 110 gallons of propane each hour. Given the high price of propane at that plant, there have been, actually, hundreds of thousands of incentives to preserve vitality and reduce costs.
Figure 1. Operation of a cross linked air/gas ratio regulator supplying a nozzle combine burner system. The North American Combustion Practical Pointers guide may be discovered on-line at https://online.flippingbook.com/view/852569. เกจวัดแรงดันnuovafima , 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 called for a price estimate to alter burner controls. As we discussed their efforts to minimize back gasoline usage, we realized smaller burners won’t be required to resolve the issue.
Oxidizer temperature is principally decided by the place of a “combustion air” control valve. Figure 1 reveals how opening that valve will increase pressure within the combustion air piping. Higher stress forces extra air via the burners. An “impulse line” transmits the air stress to one side of a diaphragm in the “gas management valve” actuator. As air pressure on the diaphragm increases, the diaphragm strikes to open the valve.
The gasoline valve is mechanically “slaved” to the combustion air being supplied to the burner. Diaphragm spring rigidity is adjusted to deliver the 10-to-1 air-to-gas ratio required for secure flame.
The plant was unable to maintain flame stability at considerably decrease gas flows as a end result of there’s a restricted range over which any given diaphragm spring actuator can provide correct management of valve place. This usable management range is recognized as the “turndown ratio” of the valve.
In this case, the plant operators no longer wanted to fully open the gas valve. They wanted finer decision of valve position with a lot decrease combustion air flows. The diaphragm actuator wanted to have the power to crack open after which management the valve utilizing considerably lower pressures being delivered by the impulse line. Fortunately, altering the spring was all that was required to allow recalibration of the gasoline valve actuator — using the present burners.
Dirty Harry would definitely 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 parts and minor rewiring were required to avoid wasting “a fistful of dollars.”
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