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Research Papers: Gas Turbines: Coal, Biomass, and Alternative Fuels

Externally Fired Micro-Gas Turbine and Organic Rankine Cycle Bottoming Cycle: Optimal Biomass/Natural Gas Combined Heat and Power Generation Configuration for Residential Energy Demand

[+] Author and Article Information
Sergio Mario Camporeale

Dipartimento di Meccanica,
Matematica e Management—DMMM,
Politecnico di Bari,
Via Re David, 200,
Bari 70125, Italy
e-mail: camporeale@poliba.it

Patrizia Domenica Ciliberti

Dipartimento di Meccanica,
Matematica e Management—DMMM,
Politecnico di Bari,
Via Re David, 200,
Bari 70125, Italy
e-mail: patriziadomenica.ciliberti@poliba.it

Bernardo Fortunato

Dipartimento di Meccanica,
Matematica e Management—DMMM,
Politecnico di Bari,
Via Re David, 200,
Bari 70125, Italy
e-mail: fortunato@poliba.it

Marco Torresi

Dipartimento di Meccanica,
Matematica e Management—DMMM,
Politecnico di Bari,
Via Re David, 200,
Bari 70125, Italy
e-mail: marco.torresi@poliba.it

Antonio Marco Pantaleo

Dipartimento DISAAT,
Università degli Studi di Bari,
Via Amendola 165/A,
Bari 70125, Italy
e-mail: antonio.pantaleo@uniba.it

Contributed by the Coal, Biomass and Alternate Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received April 6, 2016; final manuscript received August 29, 2016; published online November 8, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(4), 041401 (Nov 08, 2016) (10 pages) Paper No: GTP-16-1127; doi: 10.1115/1.4034721 History: Received April 06, 2016; Revised August 29, 2016

Small-scale combined heat and power (CHP) plants present lower electric efficiency in comparison to large scale ones, and this is particularly true when biomass fuels are used. In most cases, the use of both heat and electricity to serve on-site energy demand is a key issue to achieve acceptable global energy efficiency and investment profitability. However, the heat demand follows a typical daily and seasonal pattern and is influenced by climatic conditions, in particular in the case of residential and tertiary end users. During low heat demand periods, a lot of heat produced by the CHP plant is discharged. In order to increase the electric conversion efficiency of small-scale micro-gas turbine for heat and power cogeneration, a bottoming organic Rankine cycle (ORC) system can be coupled to the cycle, however, this option reduces the temperature and the amount of cogenerated heat available to the thermal load. In this perspective, the paper presents the results of a thermo-economic analysis of small-scale CHP plants composed of a micro-gas turbine (MGT) and a bottoming ORC, serving a typical residential energy demand. For the topping cycle, three different configurations are examined: (1) a simple recuperative micro-gas turbine fueled by natural gas (NG); (2) a dual fuel externally fired gas turbine (EFGT) cycle, fueled by biomass and natural gas (50% share of energy input) (DF); and (3) an externally fired gas turbine (EFGT) with direct combustion of biomass (B). The bottoming ORC is a simple saturated cycle with regeneration and no superheating. The ORC cycle and the fluid selection are optimized on the basis of the available exhaust gas temperature at the turbine exit. The research assesses the influence of the thermal energy demand typology (residential demand with cold, mild, and hot climate conditions) and CHP plant operational strategies (baseload versus heat-driven versus electricity-driven operation mode) on the global energy efficiency and profitability of the following three configurations: (A) MGT with cogeneration; (B) MGT+ ORC without cogeneration; and (C) MGT+ORC with cogeneration. In all cases, a back-up boiler is assumed to match the heat demand of the load (fed by natural gas or biomass). The research explores the profitability of bottoming ORC in view of the following trade-offs: (i) lower energy conversion efficiency and higher investment cost of biomass input with respect to natural gas; (ii) higher efficiency but higher costs and reduced heat available for cogeneration with the bottoming ORC; and (iii) higher primary energy savings and revenues from feed-in tariff available for biomass electricity fed into the grid.

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Figures

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Fig. 1

Scheme of the microturbine for CHP generation

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Fig. 2

Scheme of the MGT-ORC combined cycle for CHP generation

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Fig. 3

Dual fuel natural gas and biomass fired cycle, adopted as topping cycle (screenshot from Gate Cycle®)

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Fig. 4

T-S diagram of the combined cycle composed of a dual fuel EFGT and a bottoming ORC saturated and recuperative cycle

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Fig. 5

Cumulated thermal and electric load for the aggregate residential energy demand assumed for the simulations (cold climate area)

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Fig. 6

Schematic of the CHP + back-up boiler system. The bottom configuration is assumed for case B (100% biomass fuel, electricity totally fed into the grid), while the upper one is referred to cases NG and DF.

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Fig. 7

Annual CHP efficiency (η¯CHP) for the case studies A (MGT + CHP), B (MGT + ORC), and C (MGT + ORC + CHP) at different input fuels (NG: only natural gas; DF: dual fuel of biomass and natural gas; and B: only biomass); CHP operating range is assumed to be 50–100% of rated electric power. Operating strategies: BL (baseload), HD (heat driven), and electricity driven (ED); and the cold, mild, and hot climate conditions.

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Fig. 8

Fossil primary energy saving (FPES, MWh/yr) for the three system configurations and fuel inputs; baseload operating strategy and equivalent heat demand of 1600 h/y (50–80 °C)

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Fig. 9

IRR of the investments (including CHP plant and back-up boiler) for the case studies A–C, different input fuels, operating strategies, and climate conditions

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Fig. 10

NPV of the investments (including CHP plant and back-up boiler) for the case studies A–C, different input fuels, operating strategies, and climate conditions

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