coal compression

No. Coal is most efficiently burned by doing almost the opposite -- by pulverizing it and burning it, with the most efficient coal power plants being fluidized bed (meaning that the coal acts more or less as a fluid).

The heat energy output of any fuel depends on the mass of the fuel. A solid pound of coal will burn slowly and liberate about 10,000 btu of heat. Pulverize it and spread it out in air so it forms a cloud, and it will explode, burning very rapidly, but still liberating about 10,000 btu of heat. The CO2 emissions of any fuel is based on the chemistry of the fuel (its carbon content per pound or kg). Coal is mainly carbon, so it releases a lot of CO2 per pound burned. Surprising though it may seem, 12 pounds of carbon joins with 32 pounds of oxygen to form 44 lb of CO2. (As you can guess, 32 pounds of O2 is a very large volume... and the amount of air containing 32 lb of O2 is an even larger volume, because air is only 20% O2.)

Although a pound of any fuel liberates a certain amount of heat when burned, the efficiency with which that heat is converted to mechanical power or electrical power varies widely. In the most basic sense, if an engine releases a lot of hot exhaust, and conducts a lot of heat to a cooling system, it is inefficient. Some very inefficient heat engines are found in cars -- thus the hot radiator and hot exhaust. Coal power plants are about as efficient as the engine in a Prius, with about 2/3 of the fuel heat going off as waste heat. The most efficient natural gas powered power plants are about 60% efficient. They emit much less CO2 per kilowatt of electricity partly because of this better efficiency, and partly because some of the heat energy comes from burning the hydrogen in natural gas (which has four hydrogen atoms per carbon atom).

Here's some info on burning coal to produce electricity. Wikipedia has some good info on burning various fuels to produce electricity, as does the US DOE at various websites.