Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical plants and refineries. Fischer is also a part-time college professor. He is the principal reliability marketing 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 need to know your control valve’s limitations.
A client recently called for help downsizing burners on a thermal oxidizer. Changes within the manufacturing course of had resulted in too much heat from the prevailing burners. All makes an attempt to lower temperatures had resulted in unstable flames, flameouts and shutdowns. The higher temperatures didn’t hurt the product however the burners have been guzzling 110 gallons of propane each hour. Given the high cost of propane at that plant, there have been, actually, millions of incentives to conserve energy and cut back costs.
Figure 1. Operation of a cross connected air/gas ratio regulator supplying a nozzle combine burner system. The North American Combustion Practical Pointers guide could be discovered 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 venture to retrofit smaller burners was being written. One of the plant’s engineers known as for a value estimate to change burner controls. As we mentioned their efforts to reduce fuel utilization, we realized smaller burners won’t be required to resolve the issue.
Oxidizer temperature is principally determined by the place of a “combustion air” control valve. Figure 1 exhibits how opening that valve increases stress in the combustion air piping. Higher pressure forces extra air through the burners. An “impulse line” transmits the air strain to a minimum of one aspect of a diaphragm within the “gas control valve” actuator. As air strain on the diaphragm will increase, the diaphragm strikes to open the valve.
The gasoline valve is routinely “slaved” to the combustion air being supplied 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 hold up flame stability at significantly lower gas flows as a outcome of there’s a restricted range over which any given diaphragm spring actuator can provide correct management of valve position. This usable management range is recognized as the “turndown ratio” of the valve.
In this case, the plant operators now not needed to totally open the gasoline valve. They wanted finer resolution of valve place with much decrease combustion air flows. The diaphragm actuator needed to be able to crack open and then control 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 gas valve actuator — using the present burners.
Dirty Harry would positively approve of this cost-effective change to the valve’s low-flow “limitations.” เกจ์แรงดัน . No burner replacements. No important downtime. Only a few inexpensive elements and minor rewiring have been required to avoid wasting “a fistful of dollars.”
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