Research Papers: Energy Systems Analysis

Increasing the Flexibility of Combined Heat and Power Plants With Heat Pumps and Thermal Energy Storage

[+] Author and Article Information
Eike Mollenhauer

Institute for Energy Engineering,
Technische Universität,
Berlin 10587, Germany
e-mail: eike.mollenhauer@iet.tu-berlin.de

Andreas Christidis

Institute for Energy Engineering,
Technische Universität,
Berlin 10587, Germany
e-mail: christidis@iet.tu-berlin.de

George Tsatsaronis

Institute for Energy Engineering,
Technische Universität,
Berlin 10587, Germany
e-mail: tsatsaronis@iet.tu-berlin.de

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received January 9, 2017; final manuscript received October 10, 2017; published online November 30, 2017. Assoc. Editor: Tatiana Morosuk.

J. Energy Resour. Technol 140(2), 020907 (Nov 30, 2017) (8 pages) Paper No: JERT-17-1012; doi: 10.1115/1.4038461 History: Received January 09, 2017; Revised October 10, 2017

Combined heat and power (CHP) plants are efficient regarding fuel, costs, and emissions compared to the separate generation of heat and electricity. Sinking revenues from sales of electricity due to sinking market prices endanger the economically viable operation of the plants. The integration of heat pumps (HP) and thermal energy storages (TESs) represents an option to increase the flexibility of CHP plants so that electricity can be produced only when the market conditions are favorable. The investigated district heating system is located in Germany, where the electricity market is influenced by a high share of renewable energies. The price-based unit-commitment and dispatch problem is modeled as a mixed integer linear program (MILP) with a temporal resolution of 1 h and a planning horizon of 1 yr. This paper presents the optimal operation of a TES unit and a HP in combination with CHP plants as well as synergies or competitions between them. Coal and gas-fired CHP plants with back pressure or extraction condensing steam turbines (STs) are considered, and their results are compared to each other.

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Fig. 1

Overview of the analyzed energy system

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Fig. 2

Overview of the unit commitment and dispatch model

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Fig. 3

Feasible operating area of CHP plants with (a) extraction condensing ST and (b) back pressure ST

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Fig. 4

Operation of the TES for the steam PP with extraction condensing ST (left) and the CCPP with back pressure ST (right)

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Fig. 5

Operation of the TES depending on the electricity price and heat demand: (a) steam PP extr. cond. ST, (b) steam PP back pressure ST, (c) CCPP extr. cond. ST, and (d) CCPP back pressure ST

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Fig. 6

Operation of the heat pump depending on the electricity price and heat demand: (a) steam PP extr. cond. ST, (b) steam PP back pressure ST, (c) CCPP extr. cond. ST, and (d) CCPP back pressure ST

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Fig. 7

Effects of a separate and combined installation of TES and HP



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