ECONOMICAL STEAM DRIVES FOR AUXILIARY EQUIPMENT IN CHEMICAL PLANTS F. J. VONACHEN Troy Engine & Machine Company, Troy, Pa.
ENGINEDRIVEGEAREDTO AN ASPHALTMIXER; EXHAUST Is USED FOR HEATINGPURPOSES
THE
ARDLY a chemical process plant exists that does not use a t least one of the following types of so-called auxiliary equipment HORIZONTAL STEAMENGINEDRIVING A PUMP IN A PETROLEUM REFINERY in its processing operations : blowers, compressors, fans, pumps, dryers, mixers, etc. I n the boiler The average cost of driving the equipment by steam engine room are usually such auxiliaries as stokers, draft fans, and in these forty-three plants was found to be only 0.5 cent per feed water pumps. All of these need drives, but the imporkilowatt-hour. Some were as low as 0.33 and 0.26 cent, and tant question for the engineer or operating man is what type one reached an exceptional low of 0.1 cent. In the sixteen of drive is best. Mechanical requirements must necessarily processing plants, the average cost was 0.543 cent per kilobe considered. Speed ranges, flexibility, starting characterwatt-hour. I n eight of them, comparative power costs were istics, oyerload capacity-these are problems that must be available showing an average reduction in power costs of 80 settled satisfactorily. But there is another factor just as per cent as the result of changing over to steam engine drives. important: “What is the economy of the drive?” The average annual saving was $2889.00, which returned Recently a survey was made in forty-three different plants 169 per cent on the entire cost of the engine and completely using modern steam engines for driving auxiliaries to ascerpaid for the installation in an average of 14 months. tain the actual cost of the drive, not just operating cost but Details of this survey as it applies to the sixteen process total cost including maintenance and fixed charges. In view plants are given here. Reasons for the economy are disof the fact that this survey covered nineteen different kinds of cussed. They indicate clearly that, when conditions are auxiliary equipment, it is reasonably comprehensive in scope. right, modern steam engines provide exceptionally low-cost Such broad usage indicates, too, that the steam engine has power for driving auxiliary equipment. all the mechanical characteristics to make it a suitable drive for auxiliary equipment. Since sixteen of the fortyTHE following representative detailed survey covers a steamthree plants can be classed definitely as chemical processing, engine-driven gas exhauster in the plant of the New York & it is also reasonable to assume that the conclusions drawn can Richmond Gas Company, Staten Island, N. Y . : be applied generally to the chemical industry.
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VOL. 30, NO. 7
INDUSTRIAL AND ENGINEERING CHEMISTRY
774
DATA: Engine, 14 X 12 inches Maximum brake h. p., 63 a t 185 r. p. m. Average brake h. p., 40 a t 117 r. p. m. Hours operation per year, 4000 Steam pressure, 135 pounds per square inch gage (dry) Superheat, O o F. Back pressure, 9 pounds per square inch gage Feed-water temperature, 200' F. Cost of steam, 21 cents per 1000 pounds Cost of engine installed, $2427 Cost of motor installed, $1983 Extra labor to operate engine, none Purchased current cost, including demand charges, 3 cents kw-hr. Part of engine exhaust used for heating and processing, 100 per cent Has operation of engine been satisfactory? Yes
engine. When there is need for steam for heating or processing, the engine fits definitely into the picture, since it produces and maintains low-cost power for various machines such as presses, stokers, forced and induced draft fans, pumps, generators, compressors, ventilating fans, blowers, exhausters, kilns, cookers, dryers, conveycrs, line shafts, and similar equipment. Steam a t 80 to 150 pounds per square inch and higher pressures can be generated by a boiler a t only slightly greater cost than a t low pressures, since most of the heat in a boiler is
ANNUAL ENGINECOST: Depreciation, 5 per cent of $2427 $ 121.35 76.45 Average interest a t 6 per cent, $2427 X 0.0315 48.54 Maintenance, 2 per cent of $2427 (Steam consumption for average load of 40 brake h. p. is 1562 pounds p3r hour ; heat left in exhaust is 91 per cent; heat chargeable to engine is 9 per cent.) . Steam cost chargeable to engine 118.20 Lubrication cost 68.70 Extra labor None Total $ 423.24 ANNUAL MOTORCOST: Depreciation, 5 per cent of $1983 Average interest at 6 per cent, $1983 X 0.0315 Maintenance, 2 per cent of $1983 Current cost, 135,000 kw-hr. a t 3 cents per kw-hr. Lubrication cost Extra labor Total
$
99.15 62.47 39.66 4050.00 4.56
None $4255.84
ANNUAL SAVIXG: $4255.84
- 423.24
$3832.60
This will pay for extra cost of engine in less than 2 months and give a yearly return on the extra investment of 860 per cent. It will pay for the entire engine cost in less than 8 months and give a return on the entire engine cost of 157 per cent.
POWER COSTAT EXHAUSTER SHAFZ: Engine, cents per kw-hr. Motor, cents per kw-hr. (Engine power is 90 per cent cheaper) a
0.313 3.15
For 135,000 kw-hr. supplied to the motor drive.
Purchased power cost is cited here without prejudice. Purchased power has its place in industry as has the steam
TABLEI.
Field Gas Ceramics Distilling
Location
Machine Driven
Va. N. Y. N. Y. N. Y. KY. Ind.
Exhaust fan Draft fan, stoker Gas exhauster Stoker Line shaft Dryer Refrigeration compressor Blower Blower Stoker Pump Draft fan Blower Cooker Draft fa? Ventilating fan
KY.
Petroleum Chemical Wood distn. Fats Paper
a
REeULTS OF
Ill. Pa. Md. Calif. Ill. Pa. S. Dak. Ill. Pa.
Av. Comparative power costs not available.
STEAM DRIVENEXHAUSTER IN A GASPLANT
SURVEY
OF
SIXTEEN PROCESS PLANTS
Time Operated per Year Hours 8500 8000
4000 6640 3800 7632 1500 8400 8640 8280 8640 3300 8760 7800 7600 7200
Steam Engine Power Cost Der Kw-Hr. Cents 0.4 0.313 0.313 1.67 0.237 0.142 1.01 0.48 0.342 0.91 1.028 0.51 0.21 0.517 0.283 0.284 0.543
Proportionate Cheapness of Engine Power
Saving per Year
%
s,o 90 a a
8 885
....
3,832
....
.. ... ...
..
12,036
402
'3
1,076 690
53 50
23 24
57
22
3,663 562
430 83
...
15
2.889
169
14
....
....
73 65 a a
76
,.. 351
a
83 80
Yearly 0 erating Return on &me to Engine Pay f o r Investment Investment % Months 123 10 ... 137 '8
... ... ...
.. ..
.. 3
..
used to change the water into steam, and the additional amount necessary to raise the pressure is relatively small. This steam can be put through the steam engine cylinder, which serves as a reducing valve, to generate power. Depending on actual steam conditions, approximately 90 per cent of the heat in the initial steam will be present in the exhaust for heating and processing to take the place of live steam previously used. Thus the steam does double duty: (a) I n passing through the engine it generates power; ( b ) it retains approximately 90 per cent of the heat in the exhaust for heating and processing purposes. Cost of generating this by-product power consists of operating and fixed costs. Operating costs are about 10 per cent of the steam cost (the other 90 per cent of the steam cost is rightfully charged to heating cost) and lubrication cost. Fixed costs based on 20-year life are: interest on investment, say 6 per cent; annual depreciation 5 per cent; annual maintenance 2 per cent, which is ample because maintenance is very small. As a general rule, no extra operating labor is necessary with the modern steam engine. I n spite of numerous items in the cost, the total is so low that steam engines usually pay for themselves in 6 to 12 months by the saving in power cost. Some plants require steam that is free from cylinder oil. Many steam engines are being operated satisfactorily today without oil cylinder lubrication. With the cylinder properly constructed and glazed by the use of beeswax and graphite (a method that has been used for years in the highly critical marine field as well as the stationary field), it may be operated without any lubrication except possibly the introduction of a slight amount of beeswax and graphite a t infrequent
STEAM-DRIVEN REFRIGERATION COMPRESSOR IN A BREWERY
requirements of most plants, and a good plant heat balance results. There is no limit to the amount of back pressure if there is sufficient initial pressure to produce the required power within the limits of practical cylinder bores. Since this low water rate is closely maintained throughout the long life of the steam engine, the original plant heat balance is also maintained. This is important if greatest saving is to be obtained. T H E modern steam engine is suitable for a wide range of steam conditions: 20 to 400 pounds per square inch pressure, very wet steam to 750" F. total temperature, vacuum to 75 pounds per square inch and higher back pressure. It is not damaged by the usual chemical impurities in steam. Flexibility, accurate control, economy, and reliability are essential factors which are met by the modern steam engine. In variable-speed service it has a wide, smooth, easily adjusted speed range with infinitely small steps and is well adapted to automatic control. Whether the control is manual or automatic, definite speed is maintained for each point of control. I n other words, there is good regulation and, of prime importance, no hunting. Constant-speed enginesfor example, those driving generators-use the automatic governor which gives regulation within 2 per cent from no load to full load. Steam engines are also quickly started since very little warming-up is required. They can be placed in service very quickly. As to reliability, the modern heavy-duty steam engine is of rugged construction, has been continuously improved, and is fully enclosed, self-oiling, and oil-tight, so that it is quite common to have months of 24-hour continuous service a t full load without a shutdown. Its speed is conservative and conducive to long life. Compressors, fans, pumps, blowers, exhausters, dryers, and generators may be direct-connected. Only a small speed reduction is necessary to drive stokers, cookers, and conveyors. Higher speed fans, pumps, dryers, and blowers may be driven by flat or V-belts or chains. Its high starting and running torque and large overload capacity are desirable features for most installations.
STEAM-DRIVEN SET FOR GENERATING CURRENT BE USEDFOR NIGHT-LOAD REQUIREMENTS
TO
intervals. A solution of colloidal graphite in distilled water, introduced into the cylinder by a special mechanical cylinder lubricator, can also be used with success. Since the water rate (steam rate) of the steam engine remains low throughout the entire speed range and even at high back pressure, the amount of exhaust best meets the
RECEIVED April 20, 1938.
775 Y
