Utilization of District Heating Networks to Provide Flexibility in CHP Production

Abstract

Increasing penetration of intermittent renewable energy production in power systems will remarkably increase the need of flexible and controllable power generation. Subsidised renewable generation has revolutionized energy markets and brought down electricity prices leading to lack of investments to new controllable generation plants. As numerous existing thermal power generation units have been closed down, there is no doubt that all the possible flexibility available in power systems should be harnessed to stabilize the power systems. Combined heat and power (CHP) generation is widely used in district heating (DH) systems. As total heat production into the DH network needs to be balanced with the total heat consumption, this sets significant limitations to the long term power production. However, the coupling between the heat load and electric production can be decoupled temporarily by using the heat storage capacity of DH network consisting of network volume and optional heat accumulators. This paper presents the results of research work dealing with the analysis of dynamic operability of interconnected CHP plants and district heating networks. The flexibility of generation capacity was compared with the requirements set to power producers to be able to participate the Automatic Frequency Restoration Reserve (FRR-A) market. For that, two case studies were presented that include FRR-A tests in two municipal CHP plants that utilize a heat only boiler and a DH accumulator to balance the heat production variations that are caused by changes in power production. The results indicate that both cases fulfil the requirements and that the DH network operation is affected only slightly. However, the rapid power level change is a disturbance to CHP boilers and DH networks that the process components and automation systems must adapt to. Therefore these aspects must be considered carefully when applying such new operation practises in existing CHP plants.