Biogas Compression and Storage System for Cooking Applications in Rural Households

Abstract-

A project is undertaken by the College of Engineering Bhubaneswar, Odisha, India to design and develop a biogas production, purification, compression and storage system suitable for the use as a cooking gas in rural households. The biogas is produced in a floating drum type digester by the anaerobic digestion of kitchen wastes and collected by an elastic balloon. A foot lever compressor is designed, which allows the users to stand and compress using foot lever and a valve system. The final prototype is able to compress the biogas to approximately 4bar in a 0.5m3 tank. In addition to the compressor, a container with silica gel is used for removal of water vapour from Biogas and there is also a fibre container with steel wool to act as a hydrogen sulfide scrubber in-line with the inlet of the biogas to the compression system. The result showed that the system could compress biogas into a container, 4 bar pressure and operating time of 30 min.

Introduction

Biogas is becoming an increasingly important source of energy for rural areas in developing countries due to readily available organic wastes like kitchen wastes. Biogas has advantage in terms of low cost sustainable energy. Biogas is an appropriate alternative to the traditional solid and gaseous cooking fuels used by developing rural communities. Biogas digester is used to collect kitchen wastes and convert it to biogas through anaerobic digestion processes. Biogas is a clean-burning, renewable fuel that contains 50-60% methane and can be used in household cooking applications . Without an appropriate method of compression, the gas remains of a large volume and it is difficult for transport and storage.
The aim of the project is to design a system to compress and store the biogas in such a way that it will be suitable for cooking gas in rural communities. For compression of biogas we have designed a piston cylinder system i.e a modified bicycle pump which is the best compression method due to its low cost and can reach the required pressure within a short time. We have taken an air tank which is the suitable storage container for biogas.

Biogas Compression and Storage System for Cooking Applications

Need of compression and storage of Biogas
Large quantities of kitchen wastes are available at rural households. But no efforts have been made to use these wastes for the purpose of production of energy. Effort was made to use this Biogas as a source of cooking with the help of bio digesters. Due to smaller size of the plants and improper handling, the output of the gas was limited and irregular. It has always been considered only as a stand by alternative arrangement. Therefore, compression and storage system has been proposed to use the Biogas from digesters. Biogas is purified, compressed and stored in LPG cylinder which makes it easy to transport for use.

Compression mechanism
The design is established as inclined “foot pump” mechanism using bicycle pumps

Foot compressor
Our project aims at high pressure gas storage system in a pressure vessel for storing compressed gas as low cost energy. A foot compressor is built for portable service and is different from common type of reciprocating compressor. This compressor has its’ size of smallest capacity of single stage to deliver 0.015m3/min and the delivery pressure is up to 4bar.

Working Principle
The foot compressor design includes two cylinders that are supported to stand by a simple frame, based on foot-operated design (Fig.5). With this design, the container is kept stationary, which is stable and the cylinders move with the lever. The lever arm acts to give mechanical advantage and moves the two plungers through the body of the cylinders. The two cylinders are used with on-off valves to compress the biogas alternately. The valve system connects the two cylinders and allows for the variable operation of the system. The cylinders are connected in parallel, and each has two valves. One of these valves controls flow from the storage balloon, the other controls the flow of biogas to the inlet of the storage tank. Once the tank contains enough compressed gas, compression will become difficult and some of the cylinders can be disengaged in order to make pumping easier. In order to disengage a cylinder the biogas valve should be placed in the “off” position so that biogas is not pulled into that branch of the system.

Conclusion
Our research work proves that biogas production, compression and storage system is a profitable venture for the rural households where large quantities of kitchen wastes are available. It is proved that biogas can be compressed, stored in LPG cylinder and made transportable. To make biogas suitable for cooking application it is compressed up to 4 bar after purification, moisture removal and filled in LPG cylinder. In addition to the energy production, biogas plant also provides organic manure and is helpful in dealing with the problems of waste disposal and pollution free environment. We determined that the most feasible compression method is a bicycle pump. We also determined that a standard air tank is ideal for this application because it is easily available, less expensive, portable with standard fittings and resists corrosion from the biogas. Our final design was fabricated using very simple and conventional construction processes. It was constructed in a very short time of 2 to 3 days. Also, the cost of our final prototype is around Rs.3, 000/ when assembled without the biogas digester.

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Biogas Compression and Storage System for Cooking Applications in Rural Households