Heat Balance Diagram for Thermal Power Plants
What is the heat balance diagram?
The Heat Balance Diagram or HBD for a Thermal Power Plant is the basically schematic representation of the entire steam cycle from the Boiler to the High Pressure Turbines (HP), Intermediate Pressure Turbines (IP) and Low Pressure Turbines (LP) to condensing, pumps, reheaters and back to boiler.
This diagram also contains information on the properties of the steam, such as pressure, temperature, enthalpy, and mass of the steam at each junction in the line.
What information does the HBD have?
As mentioned above, the HBD or heat balance diagram has the heat equation at the points before and after each component. Taking into account the first point after the boiler, knowing the properties of the steam, the pressure and the temperatures, other properties such as the enthalpy of the steam can also be determined. Knowing the efficiencies and considerations such as pressure drop across the control valves, these properties can be determined throughout the cycle and thus the heat rate of the system. With the help of the heat rate, the required mass of steam can be determined.
Because it is important?
The heat balance diagram is usually one of the first diagrams produced, and part of the process control diagrams (PCD), by an engineering or consulting wing while working on the project (power plant) specifications. HBD helps design the plant by providing the properties of steam at different points throughout the steam cycle, thus providing vital information useful in designing the entire system and supporting systems. In a way, this diagram is essential to finalize the specifications of the different components before starting the bidding procedures by the consultants, especially when working on EPC assignments.
HBD, in fact, also helps to estimate the cost of the plant and provides the heat rate, the operating cost can also be estimated. Knowing both costs, it is easier to decide to refine the specifications of the components (comparing the initial investments and operating costs), before the bidding process, as mentioned above.
Typically, there has been no way for the project owner to comment on the consultants’ decision on specifications. It mostly has to rely on individual discretion and experience and expertise. However, recently some software solutions have come to support the engineers, which can simulate the Heat Balance Diagram for the engineers to understand the process in a better way and not just to comment on the design provided by the consultants, they also provide the opportunity to increase operating efficiencies, resulting in significant savings in operating costs. Some of these commercial programs that are based on the Rankine cycle are “Simple Heat Balance”, Thermoflow, FCycle (all from different vendors) are now available and quite accurate and affordable.