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What is biogas?

Biogas is a gas mixture which is generated when organic compounds are fermented in the absence of air (anaerobic fermentation). This gas mixture is mainly made of carbon dioxide (CO2) and methane (CH4), and is classified as hazardous greenhouse gases.

Methane is a combustible gas, usable as a bio-fuel for cooking, lighting, and generate electricity.

The biological gas plant

A plant to collect biological gas has five components: the inlet, the fermentation chamber, the gas, the gas storage bag or tank, and the outlet and the exit pipe through which the gas is removed. Organic matter such as manure (human or animal), municipal waste, duckweed or rice straw is brought into the fermentation  chamber (through the inlet). The process of anaerobic fermentation will take place here to generate biological gas (biogas). It will also produce a substrate rich in nutrients which can be used as organic fertilizer or fish feed.

The processing of manure, organic rubbish and wastewater in the plant helps to keep the environment clean. There is no longer any bad smell from sewage or livestock manure. Cooking by biogas is much cleaner than cooking over a wood fire, and there is no smoke to cause lung problems and eye diseases.

In Anaerobic Digestion for Biogas Production, the organic waste with humid and solid content are fed into a Digester with controlled

parameters such as pH, Temp, C/N ratio, organic loading rate, retention rate and mixing rate, etc.

The end biogas produced from the Digester is a biofuel commonly used to generate electricity through a gas turbine.

Generally, 1 ton of proper sorted organic waste is able to generate:-

· Approx 80 to 200m3 of biogas;

· Approx. 55/44 to 7030 of Methane/CO2;

· Approx 20.9 to 26.6 MJ/m3 of heat;

· 60 to 100 kWh of electrical power (calculated on 25% rated efficiency)

Refuse (digestate) in solid and liquid form are quality material usable as soil conditioner and organic fertilizer.

Advantage of Landfill Anaerobic

Biogas Production System:- 

1. Reduce final waste to landfill by as much as 90%;

2. Recycling of valuable material

3. Biogas power generation;

4. High grade liquid fertilizer concentrate and organic solid composting as soil conditioner;

5. Environmental protection in term of odor and leachate;

6. Sustainable Development concept;

Disadvantage of Biogas is:- 

1. High initial investment cost required for waste analysis, plant design, and construction;

2. Skill maintenance manpower required.

Incinerator

Incinerator is useful where the waste characteristic is considered dry such as the followings:-

· Moisture content of below 50%

· Calorific value higher than 4500 KJ/kg

· Combustible (volatile solid) above 25%

· Non-combustible (ash content) below 60%

In general, incineration of waste of 1 mt/d could produce heat for boiler to generate steam turbine with electrical potential of approximately 22kW per m/ton.

Advantages of Incinerator:

· Small land area required

· Waste to landfill reduction by 75%-95%

· Odorless

· CHP power generation

Disadvantages:

· High initial investment cost

· High operating cost

· Skilled manpower needed

· Additional gaseous and fly-ash treatment processes needed

Project Consideration

Construction and Operations Cost

The design criteria will ultimately drive the costs of both the construction and operation of a waste-to-energy plant. The design criteria must consider unique base-specific waste stream analyses. The energy manager should select a plant operation that will maximize the waste characteristics of the base.

Economic & Financial Analyses

The financial attractiveness of a waste-to-energy facility hinges several factors in particular local landfill tipping fees, trash transportation costs, construction and operations costs of the plant, purchase price of produced energy, recycling revenues, and interest rates.

Landfill Tipping Fee and Transportation Cost

Since 1982, the average landfill tipping fee in the United States rose from $12 per ton to $60 per ton in 2005. In some states with high population density (e.g., New Jersey), the average tipping fee ranges from $100 to $150 per ton. Most plants contract out refuse collection and disposal services.

Power Purchase Agreement

The United States Congress passed a law aimed at promoting greater use of renewable energy. The Public Utility Regulatory Policies Act (or PURPA) was a law passed in 1978 as part of the National Energy Act. This law created a market for non-utility power producers forcing state or national utility producers to buy power from these producers at the "avoided cost" rate, which was the cost the electric utility would incur were it to generate or purchase from another source. Generally, this is considered to be the fuel costs incurred in the operation of a traditional power plant.

Many countries now have similar legislation in one form or another supporting renewable energy, utilities companies are required to buy the energy generated from a waste-to-energy plant. The purchase price and conditions for sale may be regulated or open for negotiation.

Recycling Revenue

Most waste-to-energy plants require some method of front-end waste handling to ensure that only combustible materials are fed to a combustion chamber. Waste handling can by accomplished by having a sorting plant to sort out the waste either automatically or with partial human intervention. Manually presorting waste can be integrated into the trash collection process. Several different trash

bins can be provided to collect separated waste (e.g., aluminum, paper, and/or glass). This part of the production process may be incorporated in conjunction with EPA’s 3-R program i.e. Reduce, Reuse and Recycle.

EcoSynergy Solution

Containerized Composting System