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Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical plants and refineries. Fischer can additionally be a part-time school 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 got to know his limitations.” This story illustrates why you have to know your control valve’s limitations.
A shopper just lately known as for help downsizing burners on a thermal oxidizer. Changes in the manufacturing course of had resulted in an extreme amount of warmth from the existing burners. All attempts to decrease temperatures had led to unstable flames, flameouts and shutdowns. The larger temperatures didn’t harm the product however the burners had been guzzling a hundred and ten gallons of propane every hour. Given the excessive price of propane at that plant, there have been, actually, millions of incentives to preserve vitality and reduce prices.
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 online at https://online.flippingbook.com/view/852569. ตัววัดแรงดัน , Inc. 4455 East 71st Street, Cleveland, OH 44015. Image courtesy of Fives North American Combustion, Inc.
A capital venture to retrofit smaller burners was being written. One of the plant’s engineers known as for a worth estimate to vary burner controls. As we discussed their efforts to cut back fuel utilization, we realized smaller burners won’t be required to resolve the issue.
Oxidizer temperature is principally determined by the position of a “combustion air” management valve. Figure 1 exhibits how opening that valve will increase pressure in the combustion air piping. Higher stress forces more air by way of the burners. An “impulse line” transmits the air pressure to one aspect of a diaphragm within the “gas management valve” actuator. As air pressure on the diaphragm will increase, the diaphragm strikes to open the valve.
The fuel valve is mechanically “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 stable flame.
The plant was unable to maintain up flame stability at significantly decrease fuel flows as a outcome of there’s a restricted vary over which any given diaphragm spring actuator can present correct control of valve place. This usable management range is called the “turndown ratio” of the valve.
In this case, the plant operators no longer wanted to fully open the gasoline valve. They wanted finer decision of valve position with a lot decrease combustion air flows. The diaphragm actuator wanted to be able to crack open and then control the valve using considerably lower pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to permit recalibration of the fuel valve actuator — using the existing burners.
Dirty Harry 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 few cheap parts and minor rewiring have been required to save “a fistful of dollars.”
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