Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical vegetation and refineries. Fischer is also a part-time faculty 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 got to know his limitations.” This story illustrates why you want to know your control valve’s limitations.
A shopper lately known as for help downsizing burners on a thermal oxidizer. Changes in the manufacturing course of had resulted in an excessive amount of heat from the existing burners. All attempts to lower temperatures had led to unstable flames, flameouts and shutdowns. The larger temperatures didn’t hurt the product but the burners have been guzzling a hundred and ten gallons of propane each hour. Given the high price of propane at that plant, there were, literally, millions of incentives to preserve vitality and reduce prices.
Figure 1. Operation of a cross connected air/gas ratio regulator supplying a nozzle combine burner system. The North American Combustion Practical Pointers e-book could be found 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 project to retrofit smaller burners was being written. One of the plant’s engineers called for a price estimate to change burner controls. As we mentioned their efforts to reduce fuel utilization, we realized smaller burners may not be required to resolve the issue.
Oxidizer temperature is principally decided by the place of a “combustion air” control valve. Figure 1 shows how opening that valve increases pressure in the combustion air piping. Higher pressure forces extra air via the burners. pressure gauge ด้าน ดูด ” transmits the air stress to one facet of a diaphragm in the “gas control valve” actuator. As air strain on the diaphragm increases, the diaphragm strikes to open the valve.
The gas valve is automatically “slaved” to the combustion air being equipped 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 result of there is a restricted range over which any given diaphragm spring actuator can provide correct management of valve place. This usable control vary is known as the “turndown ratio” of the valve.
In this case, the plant operators not wanted to completely open the gasoline valve. They needed finer decision of valve position with much lower combustion air flows. The diaphragm actuator needed to have the flexibility to crack open and then control the valve utilizing significantly lower pressures being delivered by the impulse line. Fortunately, altering the spring was all that was required to permit recalibration of the fuel 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 project. No burner replacements. No significant downtime. Only a few inexpensive components and minor rewiring were required to avoid wasting “a fistful of dollars.”
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