SRAC Publication No. 375 Southern Regional Aquaculture Center VI May 1995 PR Powering Aquaculture Equipment J. David Bankston, Jr.1, and Fred Eugene Baker2 The choice of a power source for 8. Current and future costs. pare favorably when total costs aquacultural production is a 9. Safety. for the entire life of the unit are choice between electric motors considered. Availability of natural and internal combustion engines. While many of these factors are gas service also impacts natural In some instances a combination site specific, this publication is gas fueled internal combustion of electric motors and generators intended to help you analyze engines. Diesel, gasoline, and LPG powered by internal combustion your situation. engines can be supplied with fuel engines may be used. Internal Typical efficiencies and lifetimes from storage tanks which allows combustion engines include of power plants and accessories considerable freedom in siting the diesel, gasoline, natural gas and are listed in Table 1. power plant. liquefied petroleum gas (LPG) The speed of internal combustion engines, with diesel being the Internal combustion engines may be varied if needed most common. Each power source engines (efficiency may suffer), giving has its advantages and disadvan- them more flexibility in this tages, many of which are site and Internal combustion engines sup- respect than electric motors. On application dependent. ply a significant percentage of the other hand, internal combus- Which type of power plant you power for aquacultural opera- tion engines are sensitive to their use will depend upon your partic- tions. This is largely due to the duty cycle. Cycles of short dura- ular situation and preferences; scattered nature of power needs tion with lengthy off cycles are however, you should consider the which may make a low-cost elec- particularly detrimental to their following factors before making tric power source (electric service) performance and longevity be- your decision: unattainable. Even under these cause ofsubstantial running time conditions, electricity may com- 1. Ability to do the job. under cold-engine conditions. In 2. Reliability of power source and fuel supply. Table 1. Typical efficiencies and lifetimes of power plants. 3. Initial cost of equipment and Attainable Useful installation. Type of Pumping Equipment Efficiency Life* 4. Expected useful life. Percent 5. Convenience of operation. Right-angle pump drive (gear head) 95 15 6. Cost and ease of maintenance. Automotive engines (gasoline) 28 9 7. Cost to run the power plant. Natural gas or lpg 28 14 Light industrial engine (diesel) 25-37 14 1Louisiana Cooperative Extension Service and Sea Grant Program and Electric motors 85-92 25 2Louisiana Cooperative Extension Service, Louisiana State University Agricultural *Based on 2,000 hours per year of use. With proper maintenance and Center. fewer hours of annual use, the useful life could be increased. 1 general, internal combustion Table 2. Derated engine. engines are best suited to higher horsepower applications with Deduct Maximum Brake high annual hours of use. Fuel Type of Service Horsepower efficiency is usually better for Percent higher horsepower engines (prop- erly matched to load), and the Continuous load 20 higher fixed cost can be spread Each 1,000 feet elevation above sea level 0.3 over more operating hours. Each 10-degree rise of ambient air Selecting an internal temperature above 60 degrees F 1 combustion engine Accessories (generator, air cleaner, water pump-heat exchanger, etc.) 5 Base your selection of an engine as a power source for pumping or Fan and radiator are used 5 similar applications requiring Right-angle drive (if not used in calculating long run times on the continuous water horsepower) 3 service rating rather than on the maximum brake horsepower Allowance for wear over time 10 (bhp) rating. Be aware that many engines are tested without com- ponents such as alternators, radi- a higher percentage of fuel con- O2/hp-hour), the increased effi- ator fans or water pumps. If an sumption. ciency of the engine more than engine does not have a continu- This may be seen in the data of doubled the oxygen transfer per ous rating or its maximum rated Professor Claude Boyd, Auburn gallon of fuel (22.6 compared to brake horsepower is given, use University. This data is presented 9.5 pounds O2/gallon). Table 2 to derate the engine for in Table 3. The Specific Oxygen The engine should be maintained continuous service. Transfer Rate (SOTR) is the in good operating condition. An engine may show substan- amount of oxygen put into the Ignition, timing and carburetion dard performance if it is not water per hour. It is a measure of should be adjusted on spark-ignit- loaded properly. An internal com- the amount of aeration that can be ed engines. Diesel engines require bustion engine operates most effi- accomplished. The horsepower fuel injection timing. Have a qual- ciently at 75 to 90 percent of its requirements for the 4-inch drum ified specialist make adjustments continuous horsepower rating at with 4-inch paddle depth are to ensure the greatest efficiency its design speed. Overloading the nearly the same for both the 540 under the operating conditions. engine can seriously shorten its rpm PTO and 1,000 rpm PTO. The An additional consideration for life as well as increase fuel costs. 1,000 rpm PTO allows the tractor diesel, gasoline and LPG engines Underloading causes inefficient engine to run at a slower speed is fuel storage. Storage tanks operation. and still turn the paddlewheel at should be designed to prevent the same speed. The tractor Diesel, gasoline and propane pollution and, if a leak or spill engine is more fully loaded at the engines should be sized to the occurs, to permit cleaning up the slower speed and its efficiency is load, whether the load is a gener- fuel. For this reason, underground higher, resulting in the consump- ator or an aerator. Properly sizing tanks are usually avoided. tion of only 0.7 gallon/hour for the power source can improve the 1,000 rpm PTO compared to Above-ground tanks may need fuel efficiency. For example, in a 1.6 gallon/hour for the 540 rpm provisions to contain leaks or situation where a high horsepow- PTO. When the 4-inch drum is spills. Check with your appropri- er (85 hp) tractor powers a small lowered to a paddle depth of 14 ate regulatory agency. Fuel loss or drum (6-inch) paddlewheel, near- inches, the power requirement at adulteration can occur in storage. ly 90 percent of the fuel consump- 540 rpm changes from 4.9 to 16.9 Fuel loss could occur through tion is required to run the tractor horsepower - a factor of 3.4. evaporation, which is particularly engine and gear train at 1,800 Because the engine was more fully a problem for gasoline and may rpm, while only about 10 percent loaded, the efficiency of the lead to higher gum content of the of the fuel is used to turn the pad- engine increased. The SOTR in- fuel. Adulteration can occur by dlewheel and aerate the pond. creased from 15.2 to 45.1 pounds condensation of water vapor from When the aerator load is O /hour, a factor of 3.0; the fuel the air or, in the case of diesel, by increased by deeper paddle depth 2 consumption increased from 1.6 bacteria which feed on the fuel in or the tractor engine rpm is gallons/hour to only 2.0 gallons/ the presence of water. Proper pre- reduced by the proper gearing, hour-a factor of 1.3. Thus, even cautions such as filters, water sep- the tractor engine is more fully though the efficiency of the aera- arators, and periodic draining of loaded, and aeration accounts for tor decreased (3.1 to 2.7 pounds water from the tank should be 2 Table 3. Test results of two sizes of paddlewheels. (Power source was an 87 hp tractor.) PTO Tractor Shaft Paddle Engine Power Fuel Speed Depth Speed Reqmt. SOTR Consumption lb O2/gal lb O2/ Aerator (rpm) (inches) (rpm) (hp) (lb O2/hr) hp-hr PTO paddle-wheel 540 4 1,800 4.9 15.2 1.6 9.5 3.1 4-inch drum 1,000 4 950 4.8 15.2 0.7 21.7 3.2 540 14 1,800 16.9 45.1 2.0 22.6 2.7 1,000 14 950 16.7 45.1 1.2 37.6 2.7 PTO paddle-wheel 540 4 1,800 12.4 26.0 1.8 14.4 2.1 20-inch drum 1,000 4 950 12.0 26.0 1.0 26.0 2.1 540 14 1,800 40.2 90.0 3.0 30.0 2.2 1,000 14 950 39.0 90.0 2.3 39.1 2.3 taken to assure that the fuel deliv- volt current. Your power supplier load the motor. If motor require- ered to the engine is clean and can also advise you on the type of ments fall between motor sizes, fresh. Remember, fuel cannot be starting equipment which must be select the larger motor. For exam- stored indefinitely; it deteriorates used and equipment needed to ple, if power required is 34 hp, with age. If the fuel is not suitable protect against overloads, under- choose the 40 hp motor rather for use, even after filtration or voltage, and short circuits, and on than the 30 hp one. treatment, it must be disposed of correct wiring procedures and Electric motors vary in efficiency properly to prevent environmen- materials for safe installations. of converting electric energy to tal damage.