PRACTICAL, AVAILABLE TECHNOLOGY
First step, always the hardest Apollo Technologies, Inc. has a way to save up to 2% of the oil consumed in many electric-utility boilers: lower the exit-gas temperature 40” or more and protect the metal parts of the boiler by neutralizing the condensed acid as it forms I n the national effort to reduce our dependence upon foreign oil, an important component of our strategy has been a program of energy conservation. To the general public, conservation has come to mean reduction of energy use by the consumer. However, fuel savings through the use of more efficient operational and production methods is a concern of the major energy producers, the electrical utility industry. The recent OPEC price increases make it more important than ever to use whatever methods are available to save energy, especially where the cost of this energy-savings technology is only a small fraction of the savings that can be gained. One way to achieve such savings is to operate the boiler at lower exit-gas temperatures. Controlled studies have shown that a 40 OF reduction in exitgas temperature will allow a 1% efficiency gain. Lowering exit-gas temperatures The effect of lowering the exit-gas temperature on utility boilers in order to gain greater fuel efficiency is well accepted. The energy yield of any heat process is described as its Carnot efficiency:
where T2 is the flame temperature and TI is the exit-gas temperature. Wallace Chinitz, professor of mechanical engineering at The Cooper Union (N.Y. City), says, “Thermodynamic calculations indicate that improvements in plant heat rates of up to 3% are possible in some power plants. Most coal-burning plants, in particular, would show dramatic im1460
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provement in their operating efficiencies by shutting down or reducing the flow through their steam coils. The resulting improvement could be used to reduce fuel input requirements and/or to increase the power output from the plant. “At the moment, no real incentive exists in the industry to aim toward the former: however, the latter should have an immediate appeal since every kilowatt that can be produced internally during peak-load periods,does not have to be purchased from the outside.” Although high exit-gas temperatures are energy inefficient, it is the routine practice used by utilities to avoid corrosion problems. These arise during combustion because sulfur in the oil is oxidized to a mixture of SO2 (97-9970) and SO3 (I-3%). When the exit-gas temperature is lowered, the SO3 combines with water vapor in the flue gas, reaches its dew point. and condenses on the cooler surfaces as the highly corrosive sulfuric acid. Thus, lowering of exit-gas temperature must be done in such a manner that the sulfuric acid which deposits on cooler metal surfaces is neutralized before it
Professor Chinitz “could be used t o reditrefitel input”
can attack the metal. How exit-gas temperatures are lowered depends upon the individual utility. In some facilities. temperatures can be reduced quickly and simply by removing or bypassing the steam coils which preheat incoming air. These coils are fed by steam from the power turbines. By shutting off these coils and conserving this steam, greater performance is gained by the turbine. In other cases where steam coils do not exist, the same effect can be gained by increasing the surface area of the air heater. In many instances, heattransfer surfaces in the form of baskets have been removed. Replacement of these baskets increases heat transfer surface area and allows this heattransfer unit to operate at maximum efficiency. The combination of steam-coil removal and increasing surface area in the air heater has an additive effect on reducing exit-gas temperature. Flue gas neutralization Flue-gas neutralization to reduce flue-gas acidity is not new. Apollo Technologies (Whippany. N.J.) has successfully used this system as a cold-end, corrosion-control technique in more than 40 utilities over the past 10 years. I n essence, this powder-forniulation system containing basic oxides and ammonia releasing agents is injected before the air heater and coats the entire cold end of the boiler. Sulfuric acid may be partially neutralized in the gas phase but the bulk condenses on metal surfaces pretreated h i t h the basic oxide. h’eutralization occurs immediately. Powder does not build u p because the flue gas exerts an errosive effect on the
deposits. Thus, both the unreacted oxide and its reaction product with SO3, a neutral sulfate salt, are swept into particle-collecting devices. If the boiler system does not have such a device, the dense particles collect a t the bottom of the smoke stack. About 20% loss of oxide or neutral salt through the stack does occur. In total weight this is far less than the amount of SO3 which would have occurred without fluegas-neutralization treatment. Economics of flue-gas neutralization
Although flue-gas neutralization has been widely used, the chief motivation for adopting it in the past has not been energy savings. Rather, special problems of acid-smut emissions or corrosion and blockage of air heaters served as justifications. Now, with the 50% rise in O P E C oil prices in 1979 alone and with the planned decontrol of domestic oil, a number of utilities can now consider this technology purely for economic reasons. D. B. McMillan, manager of production at the South Carolina Electric and Gas Co., says, “A significant reduction in fuel-oil consumption was achieved when we were able to reduce the steam coil usage at the Williams Station, Columbia, S.C. With the lower exit-gas temperature allowable by chemical treatment with Apollo Coaltrol M, fuel savings were in excess of $200 000/yr, after deducting the chemical and any capital cost.” H e continued, “These savings were based on a fuel-consumption rate of 833 bbl/hr at a current fuel cost of $1 9.18/bbl. Since the injection system has been in place since 1976, the original capital cost of $80000 was absorbed in the first year’s savings.” Figure 1 documents the price history of O P E C oil since 197 1 . Figure 2 illustrates the changes in flue-gas neutralization economics that have occurred as a result of these price rises. Whereas lower priced high-sulfur oil required the utility to use this system for more than half its operating time in order to justify it economically, the more expensive oils burned today break even at 1 /3-1/6 on-line time. Incentives
The question may well be asked, why, if the technology has such favorable features, has it not been used in every instance where applicable? One can only speculate, but it is known that, as with similar technologies, the capital and operating costs must be justified to the individual Public Utility Commissions. As a consequence, the recovery of costs can by no means be guaranteed. However, the savings
FIGURE 1
-
Price history OPEC oil 197Uuly 1979 24
Allowable maximum price ------with surcharges ($23.50/bbl)
LU
-
I
Current benchmark ($1 8/bbl)
16
I
$lbbl 12
4
0 1970
I
I
I
I
I
I
I
I
I
71
72
73
74
75
76
77
78
79
80
Year FIGURE 2
Net savings at reduced exit-gas temperature with fluegas neutralizatiDn for a 5oo.W boiler 1000
-
$20/0.5%s
-
$18/0.5%s $20/1%s $16/0.5?’0 S $1 811 % S $1611?’0 s
Net savings as a function of hrslyr of operationwith oils of 0.5-, 1 -,and 2% S levels and prices of $16, $1 8, and 8oo -$201bbl. are shown. A 1% fuel savings via a 40% reduction in exit-gas temperature is assumed.
600 $1000
$2012%s
400
amos
-
$1
200
$1 612%S
0 -100
0
2,000 4,000 6,000 Hrslyr of boiler operation
Bmak-even point. For example, one would have to run the 5oo-MW boiler
3000 hdyr on 2% Soil at $iSlbbl before any savings would accrue. Another
that are achieved result in an automatic adjustment of the fuel rates, thereby leaving the utility with no economic benefits to show for its conservation efforts. Douglas Bauer, senior vice president of the Edison Electric Institute, the organization representing investorowned utilities, has commented: “By and large, most utilities would wel-
8,000
example, one would have to run the 5OO-MW boiler 2OOO hrs/yr on 2% S, $18/bbl oil before savings would accrue, etc.
come the opportunity to pursue additional energy-conservation measures. The documented savings, after deduction of capital and other costs, should be divided in an equitable manner between themselves and the consumer. I guess the bottom line for adopting a measure of this type is: Will the consumer benefit? I believe he will.” Volume 13, Number 12, December 1979
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