Robert L. Fischer, P.E., is a physicist and electrical engineer who spent 25 years in chemical crops and refineries. Fischer can be a part-time faculty professor. He is the principal reliability marketing consultant for Fischer Technical Services. He may be reached at
One of Dirty Harry’s famous quotes was: “A man’s received to know his limitations.” This story illustrates why you have to know your control valve’s limitations.
A shopper recently called for help downsizing burners on a thermal oxidizer. Changes in the manufacturing course of had resulted in too much heat from the existing burners. All attempts to lower temperatures had resulted in unstable flames, flameouts and shutdowns. The higher temperatures didn’t hurt the product but the burners were guzzling 110 gallons of propane every hour. Given the excessive cost of propane at that plant, there were, actually, millions of incentives to preserve 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 e-book can be discovered on-line at 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 called for a worth estimate to vary burner controls. As we mentioned their efforts to reduce gasoline usage, we realized smaller burners might not be required to unravel the issue.
Oxidizer temperature is mainly decided by the position of a “combustion air” management valve. Figure 1 exhibits how opening that valve increases strain within the combustion air piping. Higher stress forces more air via the burners. An “impulse line” transmits the air strain to one side of a diaphragm in the “gas management valve” actuator. As air pressure on the diaphragm increases, the diaphragm moves to open the valve.
The gasoline valve is automatically “slaved” to the combustion air being provided 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 take care of flame stability at considerably decrease fuel flows as a result of there’s a restricted range over which any given diaphragm spring actuator can provide accurate management of valve place. This usable management vary is called the “turndown ratio” of the valve.
In this case, the plant operators now not needed to completely open the gasoline valve. They needed finer resolution of valve position with a lot decrease combustion air flows. The diaphragm actuator needed to find a way to crack open and then control the valve utilizing significantly decrease pressures being delivered by the impulse line. Fortunately, changing the spring was all that was required to allow 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 vital downtime. Only เกจวัดแรงดันน้ําไทวัสดุ of cheap elements and minor rewiring had been required to avoid wasting “a fistful of dollars.”