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 college professor. He is the principal reliability advisor for Fischer Technical Services. He may 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 help downsizing burners on a thermal oxidizer. Changes within the manufacturing process had resulted in too much heat from the present burners. All makes an attempt to decrease temperatures had ended in unstable flames, flameouts and shutdowns. The higher temperatures didn’t harm the product however the burners have been guzzling a hundred and ten gallons of propane every hour. Given the high price of propane at that plant, there have been, actually, hundreds of thousands of incentives to conserve power and reduce prices.
Figure 1. Operation of a cross connected air/gas ratio regulator supplying a nozzle mix burner system. The North American Combustion Practical Pointers guide can be discovered online 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 challenge to retrofit smaller burners was being written. One of the plant’s engineers known as for a value estimate to vary burner controls. As we discussed their efforts to reduce back gas utilization, we realized smaller burners won’t be required to solve the problem.
Oxidizer temperature is mainly decided by the position of a “combustion air” control valve. Figure 1 reveals how opening that valve increases stress in the combustion air piping. Higher stress forces extra air through the burners. An “impulse line” transmits the air pressure to at least one aspect of a diaphragm within the “gas management valve” actuator. As air stress on the diaphragm will increase, the diaphragm moves to open the valve.
The gasoline valve is automatically “slaved” to the combustion air being provided to the burner. Diaphragm spring pressure is adjusted to ship the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to take care of flame stability at considerably lower gasoline flows as a end result of there is a restricted range over which any given diaphragm spring actuator can present correct control of valve place. This usable management vary is named the “turndown ratio” of the valve.
In this case, the plant operators now not needed to totally open the gasoline valve. They needed finer decision of valve place with a lot decrease combustion air flows. The diaphragm actuator wanted to find a way to crack open and then management the valve using considerably lower pressures being delivered by the impulse line. Fortunately, altering the spring was all that was required to allow recalibration of the gasoline valve actuator — utilizing the prevailing burners.
Dirty Harry would undoubtedly approve of this cost-effective change to the valve’s low-flow “limitations.” No capital project. No burner replacements. เครื่องมือที่ใช้ในการวัดความดัน . Only a few inexpensive elements and minor rewiring have been required to save tons of “a fistful of dollars.”
Share