6.7. Heat Recovery Module

6.7.1. Overview on the Heat Recovery Module

After having gathered all relevant data and having analysed the potential for energy savings through the use of energy efficient technologies, the next step within the audit methodology is a structured analyses for the potential of further energy savings by heat recovery. This is highly important as the application of any energy efficiency measures prior to the change of an energy supply system ensures an efficient overall concept for a sustainable supply of energy in the future and avoids over-dimensioning of supply equipment.

Heat integration is since the 70s (Linhoff et. Al) a well developed methodology for the optimisation of thermal processes. With the pinch analysis the potential of heat recovery can be shown within a system of energy streams. Based on the acquired data of processes and supply equipment of the company and based on the energy balance, “enthalpy streams” can be defined that show the energy demand or the energy availability of a process respectively. Such streams can be defined for any processes and equipments. Focus will lie on the thermally most relevant streams.

Based on such a stream table, the hot and cold composite curve can easily be drawn and show the theoretical maximal potential for heat recovery for a defined ΔTmin over the heat exchangers.

This theoretical potential is the basis for a technically and economically feasible heat exchanger network.

6.7.2. Basic procedure in EINSTEIN

The Heat Recovery Module in EINSTEIN is based on the data entered in the data acquisition module, including processes, energy equipment, waste heat and existing heat exchangers. On this basis the relevant energy streams of the company are defined. EINSTEIN can only calculate the energy stream based on entered data – missing values for the calculation can lead to a sub-ideal result! These energy streams are then processed in an automatic calculation of heat exchangers. This means, without interaction from the user a heat exchanger network is suggested.

The heat exchanger network that is calculated by the tool can either consider the existing heat exchangers as “non-changeable”, so the existing heat exchangers will not be changed and just the current energy demand and availability are matched in other heat exchangers. However, in case the user would like to see whether other alternatives instead of keeping existing heat exchangers exists or how the existing supply system can be optimized, the calculation can also be done without considering existing heat exchangers. This makes sense if the company is already considering changing existing heat exchanger equipment.

The energy which is saved by each heat exchanger is displayed, taking into account possible storages. The remaining energy streams are used in a following calculation of the yearly energy demand curves and energy availability curves respectively. So the remaining energy demand and the remaining waste heat demand is shown by temperature and time steps over the year.

Heat exchangers can be accepted or deleted and also changed. If energetic parameters of proposed heat exchangers (temperatures of sources, sink etc) should be changed, the user can delete the proposed heat exchanger and enter a heat exchanger with the required changes as “existing” heat exchanger in the data entry. This can later be taken as a constant heat exchanger and a new calculation on this basis will not interfere with this defined heat exchange.

6.7.3. Calculation of the heat exchanger network

The calculation of the heat exchanger network itself is done in the Design section at the menu point „HX network“. For any calculations to start press the button: „Calculate“. The heat exchanger algorithm is activated to calculate new heat exchangers. The user can choose two possibilities:

  1. to consider the existing heat exchangers in the calculation: this means that any so far entered heat exchangers will remained unchanged and new heat exchangers are suggested ADDITIONALLY. If this option is not activated, existing heat exchangers will not be considered and a completely new network is proposed.
  2. to consider the condensation heat of the boiler off gas: as this option only make sense under certain cirumstances in the company, the user can choose to activate this. If this option is not activated only the waste heat above condensation temperature of the boiler offgas is considered.