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. As numerous existing thermal power generation units have been closed down, 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 heat load and electric production can be decoupled temporarily by using the heat storage capacity of DH networks and heat accumulators. This paper presents an analysis of dynamic operability of interconnected CHP plants and district heating networks. The flexibility of generation capacity was compared with the requirements set when attending 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. The results indicate that both cases fulfil the requirements and that the DH network operation is affected only slightly. However, the rapid power level changes are disturbances 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.