Fischer: Know your valve’s limitations 

Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical vegetation and refineries. Fischer can also be a part-time faculty professor. He is the principal reliability marketing consultant for Fischer Technical Services. He could additionally be reached at bobfischer@fischertechnical.com.
One of Dirty Harry’s well-known quotes was: “A man’s obtained to know his limitations.” This story illustrates why you have to know your control valve’s limitations.
A shopper lately called for assist downsizing burners on a thermal oxidizer. Changes in the manufacturing course of had resulted in an excessive amount of heat from the present burners. All attempts to lower temperatures had led to unstable flames, flameouts and shutdowns. The larger temperatures didn’t harm the product however the burners were guzzling one hundred ten gallons of propane every hour. Given the excessive value of propane at that plant, there were, literally, hundreds of thousands of incentives to conserve power and cut back prices.
Figure 1. Operation of a cross linked 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. เกจวัดแรงดันน้ำ10บาร์ , 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 known as for a value estimate to alter burner controls. As we mentioned their efforts to reduce gas utilization, we realized smaller burners might not be required to resolve the problem.
Oxidizer temperature is basically decided by the position of a “combustion air” management valve. Figure 1 shows how opening that valve will increase strain within the combustion air piping. Higher pressure forces more air via the burners. An “impulse line” transmits the air pressure to one aspect of a diaphragm in the “gas management valve” actuator. As air stress on the diaphragm will increase, the diaphragm strikes to open the valve.
The fuel valve is mechanically “slaved” to the combustion air being provided to the burner. Diaphragm spring rigidity is adjusted to ship the 10-to-1 air-to-gas ratio required for stable flame.
The plant was unable to maintain flame stability at significantly decrease gas flows as a result of there’s a limited vary over which any given diaphragm spring actuator can provide accurate management of valve position. This usable control vary is recognized as the “turndown ratio” of the valve.
In this case, the plant operators no longer wanted to totally open the gasoline valve. They wanted finer resolution of valve place with a lot lower combustion air flows. The diaphragm actuator needed to have the flexibility to crack open and then management the valve utilizing significantly decrease pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to permit recalibration of the gasoline valve actuator — utilizing the existing burners.
Dirty Harry would positively approve of this cost-effective change to the valve’s low-flow “limitations.” No capital project. No burner replacements. No important downtime. Only a few inexpensive elements and minor rewiring have been required to save “a fistful of dollars.”
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