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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 college 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 well-known quotes was: “A man’s got to know his limitations.” This story illustrates why you should know your control valve’s limitations.
A shopper lately called for help downsizing burners on a thermal oxidizer. Changes within the manufacturing course of had resulted in too much warmth from the existing burners. All attempts to lower temperatures had led to unstable flames, flameouts and shutdowns. The greater temperatures didn’t harm the product but the burners were guzzling 110 gallons of propane each hour. Given the excessive cost of propane at that plant, there have been, literally, millions of incentives to conserve power and cut back costs.
Figure 1. Operation of a cross related air/gas ratio regulator supplying a nozzle mix burner system. The North American Combustion Practical Pointers guide can 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 referred to as for a value estimate to alter burner controls. As we mentioned their efforts to cut back gasoline usage, we realized smaller burners may not be required to solve the issue.
Oxidizer temperature is basically determined by the position of a “combustion air” control valve. Figure 1 exhibits how opening that valve increases strain within the combustion air piping. Higher stress forces more air through the burners. An “impulse line” transmits the air strain to one facet of a diaphragm in the “gas control valve” actuator. As air stress on the diaphragm will increase, the diaphragm moves to open the valve.
The gas valve is mechanically “slaved” to the combustion air being equipped to the burner. Diaphragm spring rigidity is adjusted to ship the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to maintain flame stability at considerably lower gas flows as a outcome of there is a restricted range over which any given diaphragm spring actuator can present correct management of valve place. This usable management range is known as the “turndown ratio” of the valve.
In this case, the plant operators not needed to fully open the gasoline valve. They wanted finer resolution of valve place with a lot lower combustion air flows. The diaphragm actuator wanted to have the ability to crack open and then management the valve utilizing significantly decrease pressures being delivered by the impulse line. Fortunately, altering the spring was all that was required to allow recalibration of the gas valve actuator — utilizing the present burners.
Dirty Harry would definitely approve of this cost-effective change to the valve’s low-flow “limitations.” weksler ea14 . No burner replacements. No significant downtime. Only a few cheap components and minor rewiring have been required to save lots of “a fistful of dollars.”
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