Having lots of diesel fuel to make electricity (200-800KW)is it better to use a diesel generator or a steam turbine?(Remember : the only way to produce steam is burning diesel)Does anybody know how many KWh can make per 1000gal?
Diesel generators in the 200 to 800 kW range are very common. The cost of anything above 600kW gets pretty high, but the diesel engine is much less expensive than a steam or gas turbine. The advantage to a reciprocating engine vs a turbine is that a reciprocating engine can better react to varying load conditions. Although a gas turbine is generally more efficient than a piston engine, they can not react quickly to a change in load. You also have a lot of excess machinery to utilize the high shaft speed of a turbine. There is one answer that suggests that you count the number of energy transfers. This can be a valid point, but you need to take into account the efficiency at which you are transferring your energy and how much waste heat you can recover and put to good use. A standard diesel engine turns fuel into work at about 35% efficiency, with little chance of recovering any usable waste heat. A turbine converts heat energy into work energy at about 40% efficiency. However, in the case of the steam turbine, a heat exchanger can be used to remove energy from the exhaust and preheat the boiler water, thus requiring less energy input from the diesel fuel, provided the system is at a steady state condition. In practicality, but a diesel genset.
You cannot even run a turbine from saturated steam. The blades get eroded by the water droplets, and your turbine flys apart with a big BOOM. So you would have to buy a new boiler as well as the turbine. Then you need a condenser, feed pump, piping, controller. the list goes on and on.
Neither. At these sizes, it's most efficient to use a gas turbine, in which the expanding gas of the burning fuel turns the turbine directly, rather than going through the lossy process of boiling water. A large gas turbine can be as much as 57% efficient in electricity production, which is far higher than a diesel engine. A gallon of diesel fuel contains about 130,000 BTU, or 137 megajoules (MJ). At a 55% conversion rate, that would mean 75.35 MJ of electricity. There are 3.6 MJ in a KWh, so that's 20.9 KWh per gallon of diesel, or 20,930 KWh for 1000 gallons.
