Heat Balance Diagram

What is Heat Balance Diagram?

Heat Balance Diagram or HBD for Thermal Power Station is the basically schematic representation of the whole steam cycle from Boiler to High Pressure (HP) Turbines Intermediate Pressure (IP) Turbines and Low Pressure (LP) Turbines to condenser to pumps to re-heaters and again to boiler.

This diagram also contains some information of steam properties like Pressure Temperature, enthalpy and mass of the steam at every junction of the line.

What Information the HBD has?

As mentioned above, Heat Balance Diagram or HBD has the heat equation at points before and after every component. Considering the first point after the boiler, knowing the steam properties, pressure and temperatures, other properties like enthalpy of the steam can also be determined. Knowing the efficiencies and considerations like pressure drop across the control valves, these properties along the cycle can be determined, thus the heat rate of the system. With help of heat rate, the mass of steam required can be determined.

Why it is Important?

Heat Balance Diagram is generally one of the first produced diagrams and part of Process Control Diagrams(PCDs), by an engineering wing or consultancy while working on the specifications of the project (power plant). HBD helps to engineer the plant by way of providing the steam properties at different point across the steam cycle, thus providing vital information, helpful to design the whole system and supporting systems. In a way this diagram is critical to finalize the specifications of different components before initiating the bidding procedures by the consultants, especially working on EPC assignments.

HBD, in fact also helps in estimating the cost of the plant as well as it provides the heat rate, operational cost can also be estimated. Knowing the both costs, it is easier to decide on refining the specifications of components (comparing initial investments as well as the operational costs), before bidding process, as mentioned above.

Usually there has been no ways for the project owner to comment on the consultants decision about the specifications. Mostly it has to be dependent on individual discretion and experience and expertise. However, recently some software solutions have come to provide support to engineers, which can simulate the Heat Balance Diagram for engineers to understand the process in a better way and not only to comment over the design provided by consultants, but also provide an opportunity to increase the operating efficiencies, resulting into significant saving in operational costs.

Some of such commercial software which are based on Rankine cycle are "Simple Heat Balance", Thermoflow, FCycle (All from different vendors) are now available which are quite accurate and affordable.