Archive for June 2010
Farm Power, a Skagit County renewable-energy company, will break ground on its second anaerobic manure digester – a renewable electricity-generating facility – that will serve the energy needs of local homes and businesses through Puget Sound Energy’s Green Power Program. The dairy digester, expected to go online before the end of the year, will produce up to 750 kilowatts of energy, or enough electricity to meet the needs of 500 homes.
Skagit County residents and brothers Kevin and Daryl Maas founded Farm Power in 2007 to address concerns about the health of the environment and the future of the traditional family farm. Farm Power works with local dairy farmers to build regional digesters that serve multiple farms. Anaerobic dairy digesters transform cow manure and other agricultural waste into clean, renewable energy by converting waste into methane-rich biogas needed to fuel an electric generator.
Currently, Farm Power has one digester in operation, located near Mount Vernon, Wash., which processes manure from neighboring dairy farms in Skagit County to produce up to 750 kW of energy. All of the digester’s energy output is acquired by PSE’s Green Power.
The groundbreaking will be held on Monday June 28, 2010 at 2 p.m. at 8421 Bob Hall Road, Lynden, Wash. in Whatcom County.
Source : Press Release
Digester systems that convert waste material into biogas are becoming more prevalent throughout the world. Rural farmers now have a means to produce good quality fertilizer and biogas from waste materials like manure in a cheap renewable way.
The problem is that this biogas produced is roughly 60% methane and 29% Co2 with trace elements of H2S, and is not up to the quality of 99% pure methane natural gas if the owner was planning on selling this gas or using it as fuel gas for machinery. The corrosive nature of H2S alone is enough to destroy the internals of expensive plant.
The solution is the implementation of a biogas upgrading or purification system. Biogas upgrading is a series of processes where the gas is first cleaned from contaminants and then dried, so that what is left at the end of the process is 98%+ methane fuel gas. Manufacturers that produce biogas purification systems each have their own different processes and technology that they employ to produce the sales quality gas. A few of them are detailed below.
This is the most common method of purifying biogas. Here raw biogas from the digester is compressed and fed into the scrubber vessel where passing water streams adsorb the gas contaminants leaving near pure methane. The gas is then dried by dessicant in the drier columns and exit the system as 98%+ pure natural gas.
Pressure Swing Adsorption
Otherwise known as PSA, this purification method separates the Co2, Nitrogen, Oxygen and Water from the raw biogas stream by adsorbing gases at high pressure and desorbing them at low pressure as waste. The PSA system usually consists of 4 different adsorption columns working in sequence; Adsorption, depressurizing, desorption and repressurizing.
The raw biogas is compressed and fed into the bottom of the adsorption column where it is purified. during this time the remaining columns regenerate, such that there is always 1 absorber column actively cleaning gas. PSA does not scrub hydrogen sulphide so this most be removed before it enters the compressor.
Using polyglycol (Tradename Selexol)to purify biogas is similar to the water washing method with regeneration. Selexol can adsorb hydrogen sulphide, carbon dioxide and water. However the energy required to regenerate the solution after adsorbing H2S is high, so hydrogen sulphide is removed before the process.
Raw biogas can be upgraded by various chemical reactions that remove the C02 and other contaminants from the gas stream. The chemicals such as Alkanolamines react at atmospheric pressure in an adsorption column with the Co2 and are regenerated afterwards with steam. The hydrogen sulphide must first be removed to avoid toxifying the chemicals.
Advantages and Disadvantages
Each plant type fulfills its purpose of supplying high quality natural gas for grid injection. However depending on the site location, various environmental and economic factors might make selecting a certain type of system a more sensible choice. For areas where water is an expensive resource a more appropriate choice would be a PSA or Selexol system which regenerate the adsorbent, however this has to be offset against the heat input required in regeneration.
Another important factor to consider is the methane loss associated with each design. The methane loss is measured using gas analyzers and flowmeters at the suction and discharge sides of the plant. Most plants are guaranteed by manufacturers to achieve a maximum 2% methane loss. Some recent studies however have measured between 8-10% methane loss at PSA and Selexol plant sites, possibly due to leaks and poor maintenance. Chemical systems have even lower guaranteed losses since the chemicals selectively react with the Co2 in the gas stream instead of adsorbing.
For a biogas upgrading plant the auxiliary power required to drive the compressors, pumps etc is anywhere between 3-6% of the total energy output in the form of natural gas. The cost associated with upgrading biogas also decreases with larger plant size, a smallish plant of 100 metres cubed per hour will upgrade gas at more than twice the cost of a plant outputting 200 – 300 metres cubed per hour.
A Digestor is only the beginning of the process to convert biomass into useful high quality natural gas. A biogas purification system takes the raw biogas at around 60% methane from the digester and through a special process outputs 98% methane for ether use as fuel gas or supplied to the grid. The four main upgrading processes are water washing, pressure swing adsorption, polyglycol adsorption and chemical treatment. Water washing and PSA are the most predominantly used systems in the world today. Typical energy requirements for a biogas purification system are between 3-6% of the total methane output, with smaller plants cost more to run than larger ones. As digester systems become more common around the world and people begin to catch on to biogas as a renewable source of energy, no doubt we will see more of these systems become available and more innovative designs.
Article Source: EzineArticles.com
Xebec signs Cooperation Agreement at World Expo with leading Chinese biogas environment company Qingdao Tianren
Xebec Adsorption Inc. (“Xebec”), a provider of biogas upgrading, natural gas and hydrogen purification solutions for the clean energy market, announced today that it has signed a cooperation agreement with Qingdao Tianren Environment Co. Ltd. (“Tianren”) for the development of anaerobic digestion systems that produce renewable compressed natural gas (“CNG”) vehicle fuel from waste materials. The signing ceremony took place at the Canadian Pavilion at World Expo in Shanghai in the presence of the Canadian Minister of International Trade Mr. Peter Van Loan.
Under the terms of the non-exclusive agreement, Xebec will supply biogas purification equipment for future biogas-to-CNG projects developed by Tianren. In addition, Xebec and Tianren will cooperate in a range of additional areas, including the development of financing alternatives for Chinese biogas project developers and the deployment of Tianren’s anaerobic digestion technology in markets outside of China.
“Xebec’s strategy is to partner with market leaders in the Chinese biogas market in order to accelerate the deployment of Xebec’s biogas purification solutions in the fast-growing Chinese biogas market,” said Kurt Sorschak, President and CEO of Xebec. “Tianren is one of the premier Chinese bio-energy companies designing anaerobic digesters for generating biogas from organic wastes, and we believe that the combination of Tianren’s anaerobic digestion technology and Xebec’s advanced biogas purification systems will create a market-leading solution to cost effectively produce renewable CNG from waste materials.
“The biogas market in China is poised for significant growth, as the Chinese government seeks solutions to process increasing amounts of municipal and agricultural wastes in an environmentally responsible matter. Currently there are more than 5,000 biogas digesters in China, producing some 13 billion cubic meters (m3) of biogas annually. According to the Chinese Ministry of Agriculture this number is set to increase to at least 40 billion m3 of biogas by 2020. At the same time, demand for CNG as a clean burning transportation fuel is also growing in China. The production of renewable CNG vehicle fuel from waste materials represents an exciting opportunity to create high-value renewable fuels while helping to solve China’s waste management challenges and reducing their carbon footprint,” said Sorschak.
Source : Press Release