KEH ENERGY EXPERTISE

• BOILER OPERATOR'S HANDBOOK

• STEAM TABLES

• SQUARE ROOT CHARTS

• EXCESS AIR / OXYGEN CURVE

• COMBUSTION OPTIMIZATION FORMS

• Have a question? E-mail Ken at KEH Energy Expertise

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Boiler Operator's Handbook

Operators will find plenty of help and guidance in Ken's boiler operator's handbook published by Fairmont Press. In writing it he made every effort to avoid the normal criticism of operator's handbooks. This one was written by a boiler operator for boiler operators, even though the author is an engineer. Every effort to address the operation of the plant not its engineering; you of course, will be the final judge of that.

If you've attended one of Ken's training classes you have one of these pocket size steam tables. If you don't, send Ken a stamped, self addressed envelope and he'll return it with one of these cards inside.

These steam tables are designed for operators in the Baltimore Metropolitan area because they use inches of vacuum and gage pressures (psig) instead of absolute pressures (psia) that are used on engineer's steam tables. If you happen to be operating a boiler at a site with an elevation over 500 feet the error is significant and you should obtain engineer's steam tables and learn how to correct for atmospheric pressure to get more accurate values. Over 2,000 feet these operator tables are so inaccurate that you shouldn't try using them.

The values for heat in the steam tables are called "enthalpy" and are based on the contention that enthalpy is zero in water at 32 degrees Farenheit. We could remove heat from water at that temperature but we're into steam and there's no sense in using a lower value of zero. Recall the rule that a Btu is the amount of heat necessary to raise the temperature of water one degree Farenheit? A close look at the tables reveals why we have them; water doesn't follow simple rules. The rule only applies between 69 and 70 degrees Farenheit.

Steam tables come in two forms, the card is a saturated steam table and only shows saturation conditions where steam and water are in close contact with each other and the steam and water temperatures are the same. For each pressure there is a corresponding temperature at which water boils. If you only know the pressure you can determine the temperature using the steam table; conversely, if you know the temperature you can tell the steam pressure. If you add any heat to the mixture some of the water is converted to steam and if heat is removed some of the steam will condense to water. In either direction it takes latent heat (the second column from the right) to convert a pound of the water to steam and that much is given off to convert a pound back to water. The specific volume (cubic feet per pound) for the liquid and the steam are listed so you can calulate the change in volume at the saturated conditions. Divide the values into one to get pounds per cubic foot.

Once steam is separated from water its temperature rises just like air. The difference is a varying specific heat, although you could use a specific heat of 0.5 to get a rough idea, more accuracy can be achieved using the superheated steam table. Some typical values for superheated steam are included with the tables you can download from here.

These tables include the more common operating pressures and temperatures. For more accuracy you should seek out a copy of Keenan & Keyes steam tables.

If you've attended one of Ken's training classes you know that the pressure drop in a system is proportional to the square of flow. These charts help make it easy to confirm linearity and answer questions about flows. There are two charts available, one is linear on both axis and allows you to use a pressure differential as a fraction of the full load value (divide the full load value into the measured value) on the left axis then follow a line to the curve and drop from the curve to the bottom axis to read the fraction of full load flow. flow. The table values are the fraction you get when dividing a full load value into the value you're looking at; for percent, multiply the result of that division by 100. Keep in mind that this method doesn't work with steam and air atomizing oil burners.

The second chart has a square root scale on the left axis and a linear scale at the bottom. By plotting the percent of pressure differential at the bottom for each cam position, or percent of controller output on the bottom you can produce a graph that should be a straight line for good control(linearity) I suggest plotting the pressure differential across the boiler (windbox or burner head to boiler outlet) at each cam position or percent of controller output for that application.

Divide the measured values for those at full load to get the value to enter on the chart. When dealing with gases the pressure and (except for saturated steam) temperature of the flowing fluid must be the same for each condition to be accurate.

This is another non-linear relationship that Boiler Operators should be aware of. Excess air and oxygen content of the flue gas are not directly proportional. To determine excess air quantity from an oxygen reading follow a vertical line from the oxygen reading on the bottom axis to the curve then a horizontal line to the left axis to read the quantity of excess air. Why doesn't the curve include values above 16% O2? Because values that high are ridiculous for boiler operation. If you're operating a gas turbine or reciprocating engine you would need a chart for higher values but the stack losses for values over 6% oxygen are excessive for a boiler.