The reason why a condenser is not typically placed on top of the boiler in a coal power plant to convert excess heat into electricity is primarily due to the limitations imposed by the laws of thermodynamics and the practical considerations of the power generation process.
In a coal power plant, the boiler's primary function is to generate steam by burning coal. The steam produced in the boiler is then directed to a steam turbine, where it expands and drives the turbine's blades, generating mechanical work. This mechanical work is ultimately converted into electrical energy by a generator.
After the steam passes through the turbine, it needs to be condensed back into liquid form to maintain the cycle. This condensation process usually occurs in a separate component called a condenser, which is located outside the boiler. The condenser is typically cooled using a different working fluid, often water, which absorbs the heat from the steam and converts it back into a liquid state.
The condenser's location outside the boiler allows for efficient cooling of the steam by utilizing a large surface area and cooling mediums like water or air. Placing a condenser on top of the boiler would limit the surface area available for heat transfer and could potentially lead to poor cooling efficiency.
Furthermore, the excess heat released into the atmosphere as waste heat energy serves a purpose in maintaining the efficiency of the power plant. The release of waste heat helps prevent overheating of the system and ensures that the temperature and pressure conditions within the boiler and steam turbine remain within safe and optimal operating ranges. Attempting to recover all the waste heat from the system would require additional equipment, increase complexity, and potentially lead to decreased overall efficiency.
While there are other methods to recover waste heat in certain industrial processes, the design and operation of a coal power plant follow specific principles and constraints to balance efficiency, safety, and practicality.