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 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 want to know your control valve’s limitations.
A consumer recently known as for help downsizing burners on a thermal oxidizer. Changes within the manufacturing process had resulted in an excessive quantity of warmth from the existing burners. All attempts to decrease temperatures had led to unstable flames, flameouts and shutdowns. The higher temperatures didn’t hurt the product but the burners have been guzzling one hundred ten gallons of propane each hour. Given the excessive value of propane at that plant, there have been, actually, hundreds of thousands of incentives to conserve vitality and cut back 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 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 project to retrofit smaller burners was being written. One of the plant’s engineers called for a price estimate to vary burner controls. As we mentioned their efforts to scale back fuel usage, we realized smaller burners may not be required to unravel the problem.
Oxidizer temperature is mainly decided by the position of a “combustion air” management valve. เกจวัดแรงดันภาษาอังกฤษ reveals how opening that valve will increase strain within the combustion air piping. Higher stress forces more air via the burners. An “impulse line” transmits the air stress to 1 facet of a diaphragm in the “gas control valve” actuator. As air strain on the diaphragm increases, the diaphragm moves to open the valve.
The gas valve is routinely “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 stable flame.
The plant was unable to maintain up flame stability at considerably decrease gasoline flows as a result of there is a limited range over which any given diaphragm spring actuator can provide accurate control of valve place. This usable control vary is named the “turndown ratio” of the valve.
In this case, the plant operators no longer wanted to completely open the gas valve. They needed finer resolution of valve place with much decrease combustion air flows. The diaphragm actuator needed to have the power to crack open after which management the valve using considerably lower pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to allow recalibration of the gas valve actuator — utilizing the prevailing burners.
Dirty Harry would positively approve of this cost-effective change to the valve’s low-flow “limitations.” No capital venture. No burner replacements. No significant downtime. Only a few inexpensive components and minor rewiring were required to save heaps of “a fistful of dollars.”
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