Tag: CHP

Poultry Waste to Biogas: An Overview

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Fresh poultry waste and animal manure is weighed and stored in a collection tank before its passage to the homogenization tank where the waste stream is diluted with fresh/recycled water and mechanically mixed to obtain a uniformly mixed waste stream.

The slurry is passed through a macerator to obtain uniform particle size of 5-10 mm and pumped into the primary anaerobic digester where stabilization of the waste takes place. The effluent from the primary digester is fed to the secondary anaerobic digester so as to ensure complete degradation of the waste stream.

Biogas from both the digesters are collected and sent to the biogas purification unit. Apart from water vapours, biogas contain significant amount of hydrogen sulfide (H2S) gas which needs to be removed due to its highly corrosive nature. The removal of H2S takes place in a biological desulphurization unit in which a limited quantity of air is added to biogas in the presence of specialized aerobic bacteria which oxidizes H2S into elemental sulfur.

Gas is dried and vented into a CHP unit to produce electricity and heat. The size and nature of the CHP system depends on the amount of biogas produced daily. The digested substrate is passed through screw press for dewatering and then subjected to solar drying and conditioning to give high-quality organic fertilizer.

The press water is treated in an effluent treatment plant based on activated sludge process which consists of an aeration tank and a secondary clarifier. The treated wastewater is recycled to meet in-house plant requirements.

A chemical laboratory is necessary to continuously monitor important environmental parameters such as BOD, COD, VFA, pH, ammonia, C:N ratio at different locations for efficient and proper functioning of the process.

The continuous monitoring of the biogas plant is achieved by using a remote control system such as Supervisory Control and Data Acquisition (SCADA) system. This remote system facilitates immediate feedback and adjustment, which can result in energy savings.

For more information, please email Salman Zafar on salman@cleantechloops.com or salman@ecomena.org

Thermal Processing of Agricultural Wastes

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Agricultural wastes are highly important sources of biomass fuels for both the domestic and industrial sectors. Availability of primary residues for energy application is usually low since collection is difficult and they have other uses as fertilizer, animal feed etc. However secondary residues are usually available in relatively large quantities at the processing site and may be used as captive energy source for the same processing plant involving minimal transportation and handling cost.

Agricultural wastes encompasses all agricultural wastes such as straw, stem, stalk, leaves, husk, shell, peel, pulp, stubble, etc. which come from cereals (rice, wheat, maize or corn, sorghum, barley, millet), cotton, groundnut, jute, legumes (tomato, bean, soy) coffee, coconut, cacao, tea, fruits (banana, mango, coco, cashew) and palm oil.

A wide range of thermal technologies exists to convert the energy stored in agricultural wastes to more useful forms of energy. These technologies can be classified according to the principal energy carrier produced in the conversion process. The major methods of thermal conversion are combustion in excess air, gasification in reduced air, and pyrolysis in the absence of air.

Conventional combustion technologies raise steam through the combustion of biomass. This steam may then be expanded through a conventional turbo-alternator to produce electricity. Co-firing or co-combustion of agricultural wastes with coal and other fossil fuels can provide a short-term, low-risk, low-cost option for producing renewable energy while simultaneously reducing the use of fossil fuels. Co-firing has the major advantage of avoiding the construction of new, dedicated, biomass power plant.

Gasification of agricultural wastes takes place in a restricted supply of oxygen and occurs through initial devolatilization of the biomass, combustion of the volatile material and char, and further reduction to produce a fuel gas rich in carbon monoxide and hydrogen. This combustible gas has a lower calorific value than natural gas but can still be used as fuel for boilers, for engines, and potentially for combustion turbines after cleaning the gas stream of tars and particulates. Biomass power systems using gasification has followed two divergent pathways, which are a function of the scale of operations. At sizes much less than 1MW, the preferred technology combination today is a moving bed gasifier and ICE combination, while at scales much larger than 10 MW, the combination is of a fluidized bed gasifier and a gas turbine.

Pyrolysis enables agricultural residues to be converted to a combination of solid char, gas and a liquid bio-oil. Pyrolysis technologies are generally categorized as “fast” or “slow” according to the time taken for processing the feed into pyrolysis products. Bio-oil can act as a liquid fuel or as a feedstock for chemical production. A range of bio-oil production processes are under development, including fluid bed reactors, ablative pyrolysis, entrained flow reactors, rotating cone reactors, and vacuum pyrolysis.

For more information, please email Salman Zafar on salman@cleantechloops.com or salman@ecomena.org

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