Options for cost-effective and efficient use of piggery biogas energy Project 4C-116

Abstract

Following recent increases in energy costs and to fulfil an industry commitment to reduce greenhouse gas (GHG) emissions, several Australian pork producers have recently installed on-farm anaerobic digestion systems. The biogas produced by these systems has typically been used to generate electrical and shed heating energy in combined heat and power (CHP) systems. While the mix of different energy requirements varies markedly between piggeries, some larger piggeries have reported producing biogas in excess of the volume required to satisfy on-site electrical power use, particularly if they are not operating on-site feed mills. Rather than flaring the unutilised biogas, or generating more electrical power for export to the grid (at relatively low rates of return), this review has examined the feasibility of adopting a range of alternative uses of biogas which could potentially improve on-farm energy use efficiency, in a cost effective manner.

A literature review was prepared providing background information on the status of biogas technology adoption in the Australian pork industry and outlining typical piggery biogas composition and properties, volatile solids (VS), biogas and methane production, seasonal variation and biogas energy estimates. Biogas use technologies identified in the literature review included: flares, boilers, internal combustion engines, electrical generators, microturbines, Stirling motors, organic Rankine cycle systems, fuel cells, cogeneration and trigeneration systems (providing cooling in addition to electrical energy and heat), vehicle fuel applications and biogas upgrading. The literature review suggested that these technologies could be used for biogas use applications such as odour mitigation, shed space heating, underfloor hot water circulation, radiators, radiant heaters, shed cooling, absorption chilling, drinking water chilling and snout cooling.

Five commercial piggery units having distinctly different pig capacities, herd compositions, and climatic conditions were selected for preparing biogas system Feasibility Studies. Site visits were carried out to gather relevant data relating to the pig herd, production and energy use at the five piggery units. These data were used to estimate typical dimensions and costs of constructing purpose-built covered anaerobic lagoons (CALs), and the biogas, methane and energy production potential, at each site. A range of biogas use options involving the generation and use of thermal and electric energy were investigated for each piggery and estimates of capital and operating costs and returns were provided in the Feasibility Studies.

The options resulting in the highest returns on investment (RoI) at each site ranged from the installation of a 50 kWth boiler at a 2143 standard pig unit (SPU) breeder unit, to a 230 kWe cogeneration unit at a 24,838 SPU combination finisher + farrow to finish unit. The other recommended piggery biogas use options employed a combination of hot water boilers and cogeneration units. The resulting overall RoIs ranged from 12 to 25%, indicating simplistic payback periods of four to eight years. These returns did not include the cost of constructing/installing the CALs and associated control equipment, or the estimated returns from the sale of Australian Carbon Credit Units (ACCUs).

It is anticipated that this research, which was carried out under Pork CRC Subprogram 4C – Carbon-Neutral Pork Production, will assist producers and industry service providers in planning and implementing biogas capture, treatment and use systems and in selecting a range of practical, cost-effective uses for the available biogas at Australian piggeries. The application of the options outlined in this report will improve the economic viability of biogas collection and use, while mitigating industry carbon emissions and reducing farm energy and hence production costs