Fischer: Know your valve’s limitations 

Robert L. เพรสเชอร์เกจน้ำ , 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 consultant 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 should know your control valve’s limitations.
A shopper just lately known as for assist downsizing burners on a thermal oxidizer. Changes within the manufacturing process had resulted in an extreme amount of warmth from the present burners. All makes an attempt to lower temperatures had led to unstable flames, flameouts and shutdowns. The larger temperatures didn’t hurt the product however the burners were guzzling 110 gallons of propane each hour. Given the excessive price of propane at that plant, there were, actually, millions of incentives to preserve vitality and cut back costs.
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 found 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 called for a worth estimate to change burner controls. As we mentioned their efforts to minimize back gas usage, we realized smaller burners won’t be required to resolve the issue.
Oxidizer temperature is principally decided by the position of a “combustion air” control valve. Figure 1 shows how opening that valve increases pressure in the combustion air piping. Higher strain forces more air by way of the burners. An “impulse line” transmits the air pressure to a minimum of one facet of a diaphragm in the “gas management valve” actuator. As air stress on the diaphragm will increase, the diaphragm moves to open the valve.
เพรสเชอร์เกจnuovafima is routinely “slaved” to the combustion air being provided to the burner. Diaphragm spring rigidity is adjusted to deliver the 10-to-1 air-to-gas ratio required for secure flame.
The plant was unable to take care of flame stability at significantly decrease gasoline flows because there’s a restricted vary over which any given diaphragm spring actuator can provide correct control of valve position. This usable management range is recognized as the “turndown ratio” of the valve.
In this case, the plant operators not needed to completely open the gas valve. They wanted finer resolution of valve place with much lower combustion air flows. The diaphragm actuator wanted to be able to crack open after which 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 gas valve actuator — using the present burners.
Dirty Harry would undoubtedly approve of this cost-effective change to the valve’s low-flow “limitations.” No capital challenge. No burner replacements. No vital downtime. Only a few inexpensive components and minor rewiring had been required to keep away from wasting “a fistful of dollars.”
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