Experimental and numerical analysis of a micro scale cogeneration system with 100 kW straw-fired boiler

Maciej Żołądek, Krzysztof Sornek, Rafał Damian Figaj, Mariusz Filipowicz

Abstract


Straw-fired batch boilers, due to their simple structure and low operating costs, are an interesting option for heating systems
dedicated to use in houses, farms, schools, industrial facilities and other buildings. Commercially available solutions include
typical water boilers and air heaters with a thermal oil jacket. The high temperature of thermal oil (180-200C) mean straw-fired
devices can be used as a source of heat for micro scale cogeneration and trigeneration systems.
The first part of this paper shows an experimental analysis of a micro scale cogeneration system based on modified
Rankine Cycle operation. A 100 kWth straw-fired batch boiler with thermal oil jacket was used as a high temperature heat
source. Thermal oil, heated in the boiler, was transferred respectively to the evaporator, superheater and oil/water emergency
heat exchanger. The steam generated was conditioned and used to power a 20 hp steam engine. Cooling water, heated in
the condenser, was pumped to a 4 m3 water tank connected to two air coolers. Control of the system operation was realized
using a dedicated automation system based on the PLC controller.
In the second part of this study, a micro scale cogeneration system was developed and modelled in TRNSYS software
on the basis of the experimental installation. The dynamic operation conditions in terms of temperatures and powers were
analyzed for the main components of the system (boiler, evaporator steam engine, condenser). Moreover, some modifications
in the system construction were proposed to improve its performance.
The results of the experimental tests were used to identify the main aspects of the considered system—temperature,
pressure and power levels in oil, steam and water circuits and operating parameters of the steam engine. Dynamic simulations
performed in TRNSYS pointed to the nominal operation scenario for the tested system and showed the great potential for
further improvements in the system construction.


Keywords


micro cogeneration, renewable energy sources, trigeneration, biomass, straw-fired boiler, TRNSYS, dynamic simulations,

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