Sim Labs for Thermodynamics and Thermal Power Plant Simulator (Beyenir and Boskovic)

This Simulator laboratory (SIMLAB) book was created to provide ancillary resources for Thermodynamics and Thermal Power Plant Simulator courses. It is intended to act as a collection of exercises to help our students merge the theory covered in the classroom with the practice performed in the labs.

Theory

First we define efficiency. There are many ways to present it, for example, efficiency is the ability to do something without wasting energy, effort or time. Put it mathematically, it is the ratio of useful output to thermal energy input. Layperson often uses the terms efficiency and effectiveness interchangeably however efficiency is to do with minimizing waste and effectiveness to do with maximizing output (more on this in Heat Exchangers Lab). Boiler efficiency is sometimes defined as combustion efficiency which is computed by the ratio of the burner’s capability to burn fuel completely to the unburnt fuel and excess air in the exhaust. Thermal efficiency on the other hand, indicates the heat exchanger’s (i.e. boiler’s) capacity to transfer heat from the combustion process to the water or steam in the boiler. In general, the maximum boiler efficiency attainable from a boiler depends on such factors as method of burning the fuel, design of the furnace and heat transfer surfaces. In addition, the type of fuel, boiler load and operational practices influence the boiler efficiency. In this lab, we focus on the fuel type, boiler load and best practices.

Theory

Recall from the First and Second Law of Thermodynamics that the adiabatic process where entropy remains constant provides the maximum energy for work. As shown on the H-S coordinates, the difference in enthalpy, (H -H ), is maximum when the lowest enthalpy (H ) is reached at the exit conditions. The ideal expansion is, therefore, a vertical line.

The difference in enthalpy H -H is called the reheat factor and is the basis for multi-stage turbines. As can be seen on the Mollier diagram, the pressure curves are divergent. This means that the higher the pressure drop in a single stage turbine the greater the reheat factor and in turn the lower the turbine efficiency. However, if the steam is expanded through multiple stages and between each stage the steam is reheated, higher turbine efficiencies can be achieved. We will see this effect later in the Power Plant Efficiency lab.

High-pressure steam leaves the boiler and enters the turbine. The steam expands in the turbine and does work which enables the turbine to drive the electric generator. The exhaust steam leaves the turbine and enters the condenser where heat is transferred from the steam to cooling water. The pressure of the condensate leaving the condenser is increased in the pump thereby enabling the condensate to flow into the boiler. This thermodynamic cycle is known as the Rankine Cycle.