Biomass and bio-energy utilisation in a farm-based combined heat and power facility

doi:10.1016/j.biombioe.2016.03.005

Biomass and Bioenergy

Volume 89, June 2016, Pages 172-183

https://doi.org/10.1016/j.biombioe.2016.03.005 Get rights and content

Highlights

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On-farm generation of energy from renewable sources reduced fossil fuel energy use.
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Renewable energy displacement of fossil fuels achieved financial benefits.
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Renewable energy systems reduced emissions of CO2.
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Poorly co-ordinated maintenance and repair adversely affected energy production.
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Farm renewable energy systems can be considered a positive GHG mitigation option.

Abstract

Five different renewable energy technologies located at an agricultural and environmental research centre in Northern Ireland, were monitored to assess the cost, performance and efficiency in real-time operation of solar and bio-energy produced from crops and farm wastes utilised for energy generation in industrial grade equipment. Monitoring was conducted over a six year period, with power units running simultaneously or intermittently according to demand from the local district heating system. The purpose of the work was to investigate fossil fuel (oil) displacement, carbon dioxide emission (CO₂e) reductions, financial and environmental sustainability of these technologies in a farm based scenario. Between 2009 and 2014, total heat output from the centre was 7.75 GWh with contributions of 47.2%, 17.1%, 9.8% and 13.5% from the biomass, biogas, multi-fuel boiler and biogas CHP unit respectively. Solar thermal produced 0.49% and the back-up oil boiler 11.9%. Total electrical output was 572.6 MWh with 95.2% generated from biogas CHP and 4.8% from the solar PV system. Fossil fuel and average CO₂e reductions ranged from 20.1% to 54.1% and 23.3–55.7% respectively, reductions that combined with financial savings to present a viable and sustainable renewable energy system.

Introduction

The increasing demand for renewable sources of energy for heating and electrical power generation, has been driven by a number of factors but largely by rising costs, fuel security issues and increasingly, environmental concerns [1], [2]. The European parliament has been instrumental in addressing these issues across all its member states and seeks to increase the uptake of biomass for energy generation and greenhouse gas (GHG) emission reductions [2]. While this may encourage interest and uptake of sustainable and renewable energy generation, there is often a mismatch in fuel availability and power plant suitability [2], [3]. Between the extremes of small scale domestic and large scale regional heat and power generation, there is often a need for intermediate sized plants and this may be particularly applicable for farm based agricultural enterprises [4], [5]. Mixed farms, such as those that have both livestock and arable capabilities, can offer high potential for both electricity and heat generation from animal wastes and crops grown specifically for energy crops. Anaerobic digestion (AD) can utilize animal wastes and crops, such as grass silage and maize silage, to produce biogas that can then be used for heat and/or electricity production. A significant and growing number of such plants running on these fuel types are already installed on farms across Europe [6], [7]. Farm buildings and their environments are often also particularly suited for solar heating and electricity production [5]. Electricity producing solar photovoltaic (PV) and heat producing solar thermal panels offer reliable and relatively continuous (during daylight hours) electricity and hot water production and are particularly suitable for farms [5]. Heat from biomass is dominated by wood fuels, from waste streams (forestry, sawmill, furniture manufacturing) and dedicated wood crops, particularly short rotation (3 year) coppice (SRC), primarily willow (Salix spp) and short rotation (12–15 + years) forestry crops such as poplar (Populus spp) and eucalyptus (Eucalyptus spp) [5], [8]. However, herbaceous crops, such as miscanthus (Miscanthus spp) commonly referred to as elephant grass, are also gaining acceptance as alternative fuels for combustion [9].

These types of modern renewable energy technologies are often installed as stand-alone plants though combined technology plants may be feasible on farms, both for primary energy supply and as a potential diversification into energy (heat and power) export [5], [10], [11]. Where such combined energy generation plants might be installed, comprehensive computerised energy management and control systems may be essential for reliable and overall efficient performance [10], [12]. However, the critical challenge for such on-farm renewable energy schemes is to achieve viable economic energy production that is environmentally sustainable and reduces GHG emissions [10], [11].

Agriculture is responsible for an estimated 28% of Northern Ireland's (GHG) emissions and the regional production of electrical energy (from mainly coal and natural gas) contributed 18.8% to total 2011 GHG emissions [13]. In the United Kingdom (UK) targets for GHG emissions reduction (35%), fossil fuel substitution and higher renewable energy reliance have led to an increased interest in renewable energy technologies. The adoption of renewable energy technologies is a mitigation strategy that has the potential to reduce emissions by replacing fossil fuel consumption and a number of incentives have been developed to enable this goal to be achieved. Currently, there are uncertainties regarding the impact of changes in farming practices on emissions from renewable energy crops and the utilisation of conversion technologies. Concerns also exist over potential conflicts between land used for fuel rather than food and the subsequent mitigation of GHG emissions by producing and utilising such energy crops for heat and/or electricity [14].

The aim of this paper is to describe and assess the measured outputs and overall performance of the inter-linked and wholly contained multiple energy production units on a large scale farm and environmental research centre in Northern Ireland. Further objectives of this study are to estimate the fossil fuel use reduction, GHG emissions and carbon savings of the research centre from its activities during a period of 6 years. This follows the adoption of renewable energy technologies in 2008 to substitute a significant proportion of fossil fuel use.

Section snippets

Site description

The schematic (Fig. 1) shows the outlay of the purpose built energy centre located within the research farm estate of the Agri-Food and Biosciences Institute, (AFBI) at Hillsborough (54.4° N and 6.0° W) in Northern Ireland.

The research farm estate has 310 ha of land with a total grassland area of 292 ha used by dairy, beef, sheep and pig production and 10 ha for biomass crop research (Fig. 2). There is also ∼200 ha of mixed broadleaf and conifer woodland, the latter being largely commercial

Electricity from biogas

Electricity outputs from this unit were generally maintained due to the continuous supply from the AD system with excess gas being used in the biogas boiler for heat. Until 2011 the plant digested an average 20 Mg d⁻¹ cattle slurry average 6.9% dry matter mass fraction) producing an average biogas output of 15.2 m³ Mg ⁻¹ slurry with an energy value of 85 kWh. By comparison fresh grass silage was found to have significantly higher energy content than dairy cow slurry, on average grass silage

Electricity production and usage

Electrical output from the CHP unit totalled 572.6 MWh for the reported years with an average monthly output of the unit 10.2 ± 2.6 MWh. The unit often ran for long periods (up to 60 days) for an average 16.3 ± 2.5 h d⁻¹, often without interruption and fault at near full load capacity producing at an average rate of 21.5 ± 0.5 kW, indicating that the gas quantity and quality was sufficient and consistent, as reported previously [21], [22]. The CHP power generation ended in December 2013 due to

Conclusions

The operational results reported in this study from a farm based combined heat and power facility, have shown that the displacement of fossil fuel and reduction of CO₂ emissions by the biomass, biogas and solar renewable energy systems, have achieved considerable financial savings and environmental benefits. That these were seen to actually continue year on year, has validated the adoption of these technologies at this particular type of medium scale farm enterprise. However, ineffective and

Acknowledgements

This work was funded by the Department of Agriculture and Rural Development for Northern Ireland (DARD). Support from the AFBI Environment and Renewable Energy Centre staff is also appreciated.

The most valuable and important scientific and technological assistance from the following EREC staff is also acknowledged; Geoffrey Meeke, George Alexander and Tom Meredith. Special thanks to Dr Scott Laidlaw (PHd) for manuscript proof reading.

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Research paperBiomass and bio-energy utilisation in a farm-based combined heat and power facility

Highlights

Abstract

Introduction

Section snippets

Site description

Electricity from biogas

Electricity production and usage

Conclusions

Acknowledgements

Biomass Bioenergy

Biomass Bioenergy

Biomass Bioenergy

Biomass Bioenergy

Renew. Sustain. Energy Rev.

Bioresour. Technol.

Bioresour. Technol.

Bioresour. Technol.

Energy Policy

Biomass Bioenergy

Biomass Bioenergy

Energy Convers. Manag.

Energy

Biomass Bioenergy

Fuel Process. Technol.

Biomass Bioenergy

Research paper
Biomass and bio-energy utilisation in a farm-based combined heat and power facility