Power-to-heat integration in a combined heat and power installation to provide flexibility to the Dutch grid

Abstract

The increase in the share of renewable energy sources in the Dutch energy mix, requires an increase in flexibility from the power consumers and producers. A key issue in the availability of wind and solar power that it is independent of the power demand. Fortunately, the liberalised power market provides a financial incentive to increase both upward and downward flexibility.

Delesto is a company that supplies process steam at ChemiePark Delfzijl. They are looking into the possibility to integrate power-to-heat (P2H) in their Combined Heat and Power installation (CHP). This would open up the possibility to decrease the power output of the plant beyond deep part load conditions, and to save on overall fuel consumption. This would be beneficial for periods where profits made from power production drops below the cost of fuel consumption. For this research it is assumed that the power used is emission free, as it originates from renewable energy sources.

In this study, the technical and financial feasibility of an hybrid configured combined heat and power plant, in which both gas and power are used to produce process heat, is researched. The CHP consists of a gas turbine (GT), a dual pressure heat recovery steam generator (HRSG) and a steam turbine (ST). Eight different configurations that offer P2H functionality to the CHP are being assessed. The electric heater concepts are compared to the 'conventional' part-load of the CHP. Their steady state behaviour is evaluated using parameters such as Additional Flexibility (AF) and Effectiveness of fuel saving ($\varepsilon$). A duct heater inside the HRSG offers the greatest AF, whereas an air preheater upstream of the GT performs best in terms of effectiveness. Additional to the initial eight electric heater concepts, the combinations of air preheater with other promising electric heater concepts are evaluated.

A dynamic study of (a part of) the HRSG including an electric heater is performed. Only the most promising electric heater concepts in terms of the steady state behaviour are reviewed. From this dynamic study it can be concluded that the minimum ramp time is of the HRSG is well within the requirements of the grid operator. However, a high pressure boiler parallel to the high pressure evaporator of the HRSG results in relative high temperature drop in the system compared to the other electric heater concepts, and is therefore removed from further consideration.

From a financial analysis, a business case is constructed for an air preheater, a duct heater, a stand-alone boiler and their combinations. It is apparent that the profits obtained at the spot market are negligible compared to the profits obtained at the imbalance market. Transportation costs are relatively high and have a damaging effect on the business case. The payback period of the air preheater is the shortest and the payback period of the duct heater the largest.