Fischer: Know your valve’s limitations 

Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical crops and refineries. Fischer can additionally be a part-time faculty professor. เกจวัดแก๊สหุงต้ม is the principal reliability advisor for Fischer Technical Services. He could also be reached at
One of Dirty Harry’s famous quotes was: “A man’s received to know his limitations.” This story illustrates why you should know your management valve’s limitations.
A client lately known as for help downsizing burners on a thermal oxidizer. Changes in the manufacturing process had resulted in an extreme amount of warmth from the prevailing burners. All attempts to lower temperatures had resulted in unstable flames, flameouts and shutdowns. The greater temperatures didn’t harm the product however the burners were 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 scale back costs.
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 can be found online at 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 referred to as for a value estimate to vary burner controls. As we mentioned their efforts to reduce gasoline utilization, we realized smaller burners may not be required to unravel the issue.
Oxidizer temperature is basically decided by the place of a “combustion air” control valve. Figure 1 reveals how opening that valve increases stress in the combustion air piping. Higher strain forces more air through the burners. An “impulse line” transmits the air strain to a minimal of one aspect of a diaphragm in the “gas control valve” actuator. As air stress on the diaphragm increases, the diaphragm strikes to open the valve.
The gasoline valve is routinely “slaved” to the combustion air being provided to the burner. Diaphragm spring pressure is adjusted to deliver the 10-to-1 air-to-gas ratio required for steady flame.
The plant was unable to maintain flame stability at significantly decrease fuel flows because there is a restricted range over which any given diaphragm spring actuator can present correct control of valve place. This usable control range is named the “turndown ratio” of the valve.
In this case, the plant operators not wanted to totally open the gas valve. They needed finer resolution of valve place with much lower combustion air flows. The diaphragm actuator wanted to have the power to crack open and then control 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 gasoline valve actuator — using the existing burners.
Dirty Harry would definitely approve of this cost-effective change to the valve’s low-flow “limitations.” No capital challenge. No burner replacements. No significant downtime. Only a number of cheap components and minor rewiring have been required to save “a fistful of dollars.”

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