Friday, December 24, 2010
The digester is covered to contain odours, maintain temperature, keeps air out and to collect the gas. Fixed covers are more usual than floating covers. During normal operation, there is a space for gas collection between the cover and the liquid surface of the digester contents. The cover of a digester has certain unique features that the operating staff must be aware of, for example, how the variation in pressure and the level inside the digester may affect the cover. The biggest danger associated with the operation of fixed cover digesters occurs when the pressure relief device mounted on top of the digester fails or the sludge overflow line blocks and the liquid level in the digester continues to rise. In such a situation, the excess gas pressure inside the digester can exceed the maximum design pressure and damage the cover or its mountings. Fixed covers can also be damaged by excess negative pressure (vacuum) or if the rate of waste sludge withdrawal exceeds the feed rate or the vacuum relief device fails.
The function of the pressure relief device is to allow pressure that exceeds a safe level to escape from the digester. The manufacturer's specifications should provide the following information to enable the operating staff to control the gas system safely. (a) The system's normal operating pressure (mm water gauge). (b) The pressure at which the pressure relief device should operate. (c) The rated gas flow capacity of the pipes.
A gas system generally comprises three pressure relief devices; one mounted on the cover of the digester, one on the gas holder and one situated at the end of the gas line before the gas burner. This device releases gas to the waste gas burner before the design gas pressure of the digester cover is reached.
The vacuum relief device functions in the opposite manner to the pressure relief device and allows air to enter the digester in the event of the waste sludge being withdrawn too rapidly. Air should not, under normal conditions, be allowed to enter the digester because a mixture of air and methane is potentially highly explosive.
Gas leaving the digester is almost saturated with water vapour. As the gas cools, the water vapour condenses causing problems. The problem is more severe when digesters are heated. To solve the problem it is essential to remove as much of the moisture as possible before the gas comes into contact with the gas system devices. For this reason, water traps should be located as close to the digester as possible. All piping should be sloped a minimum of 1% towards the water trap, which should be situated at a low point in the gas line.
Flame traps are emergency devices installed in gas lines to prevent flames travelling back up the gas line (flashback) and reaching the digester. The flame trap generally consists of a box filled with stone or a metal grid. If a flame develops in the gas line, the temperature of the flame is reduced below the ignition point as it passes through the trap and the flame is extinguished.
Pressure regulators are used when a lower pressure than the system operating pressure, is required for a specific device such as a boiler water heater or incinerator. Regulators maintain a constant gas pressure at the point of use
The rate of gas production is probably the most sensitive process control indicator at the disposal of the operating staff. Gas meters should be regularly serviced so as to give accurate and reliable gas readings. Every effort should be made to have the gas meter calibrated every six months.
Check valves (non-return valves) are installed in the gas line to allow gas flow in one direction only i.e. out of the digester.
Gas pressure gauges indicate the pressure in the gas system and assist in locating any blockages in the line. If a blockage occurs, a pressure reading downstream will register a lower pressure than that of a gauge upstream.
The pressure relief device at the waste gas burner safely flares excess gas to the atmosphere and thus reduces the potential for a dangerous accumulation of gas in the system.
Many anaerobic digestion waste treatment plants have a means of storing excess gas. This can be in the form of either a floating roof on the digester or a separate gasholder.
A mixture of biogas and air can be explosive. Methane gas in concentrations of between 5% and 15% in air by volume is explosive. Operating staff on waste treatment plants should ensure that no air is allowed to enter the digester or gasholder. All piping and equipment must be sealed properly to prevent gas from escaping to the outside. There must be no smoking and all electrical installations, including light switches, torches etc must be of the explosion-proof type, as the smallest spark could ignite escaped gases.
Your Independent guide to Waste Treatments [http://waste-treatments.com]
Wednesday, December 22, 2010
Sludge Digestion Tanks
A sludge digestion tank is an R.C.C. tank of cylindrical shape with a hopper bottom and is covered with a fixed or floating type of roof. The latter makes the digestion of sludge much more effective. The weight of the cover is supported by sludge, and the liquid forced between the tank wall and the side of the cover provides a good seal. The raw sludge is pumped into the tank where it is seeded with digested sludge.
On undergoing anaerobic digestion, gases of decomposition (chiefly Ch4 , CO2) are given out by the anaerobic digester. Sludge gas rises out of the digesting sludge. It moves along the ceiling of the cover and collects in the gas dome. The cover can float on the surface of the sludge between the landing brackets and the overflow pipe. Rollers around the circumference of the cover keep it from binding against the tank wall.
The digested sludge, which settles down to the bottom of the tank is removed under hydrostatic pressure periodically, say, once a week. To maintain optimum temperature, the tank is generally provided with heating coils through which hot water is circulated.
The supernatant liquor i.e., the part of the tank content lying between the scum and the sludge is withdrawn at the optimum level through a number of withdrawal points located at different elevations of the tank. As it is high in BOD and suspended matter contents, it is sent back to the incoming raw sewage for undergoing re-treatment. During the digestion of sludge, the scum formed at the surface gets broken up by the recirculating flow or through mechanical rackers called scum-breakers.
The amount of sludge gas produced during digestion of sludge varies from 0.014 to 0.028 m3 per capita with 0.017 m3 being quite common. The gas produced contains 65 per cent of methane with a calorific value 5400 -- 5850 kcal. m3, 30 per cent of carbon dioxide and balance 5 per cent of nitrogen and other inert gases. It resembles natural gas and may be used as a fuel for cooking. Principal uses however, are for driving gas engines, and for heating sludge to promote quick digestion of sludge.
For a free eBook on a great new wastewater treatment technology and for everything else you want to know about wastewater treatment including digestion of sludge, click http://www.all-about-wastewater-treatment.com.
Richard J. Runion is the President of Geostar Publishing & Services LLC. Rich loves net research & blogging. His new blog on Wastewater Treatment is fast becoming popular, as it is comprehensive and well-researched.
Tuesday, December 21, 2010
Physic nut seed contains the oil around of 25-35% of the total unit weight. This form of waste has a crude oil content of 75-65%. Waste can be processed into solid fuel through a process of densification. The process of carbonization or non-carbonization can also be applied to improve the quality of these solid fuels.
In the carbonization process, waste is inserted into the reactor in order to remove moisture, volatile matter and tar. After this process, they are sent to the densification process. This process forms the material into briquettes using a press machine.
There are two types of press machine used, is hydraulic and screw machine. Densification product is densified material called briquettes. This fuel can be used as solid fuel. Briquettes can be easily burned into the furnace or conventional stove. In commercial production, briquettes used to burn water in the boiler. Steam generated, is sent to a steam turbine. This steam spins the generator wheel to produce electricity.
Gas fuel from physic nut wasteThe gas fuels can be produced through an anaerobic digestion process. This process is a chemical process involving microorganisms without the presence of oxygen in a digester. This process produces the methane, carbon dioxide, hydrogen, nitrogen, hydrogen sulfide and a small amount of gas. Methane is the largest composition compared with other gas products. This process can be classified into two types: dry and wet anaerobic digestion. The Differences between these anaerobic processes are the ratio of biomass and water used in the digester.
Nugroho Agung Pambudi has been writing articles including papers for nearly 3 years now. His journal papers can be reached both international journal and conference.
Sunday, December 19, 2010
The report found that if complete grid-connectivity were achieved, the following incomes could be generated:
2 wind turbines: 300,000 Anaerobic digester: 460,000 Hydroelectric Installation: 190,000 Solar Panels: 26,300
The total income for these renewable projects would be an impressive 916,000 with a potential of 18.5m to be made over the project's lifetime.
The potential for landowners to benefit from feed-in tariff legislation in the UK is enormous with the potential not only to receive tariff payments but also to significantly reduce overheads by using the energy produced on the land.
The Knight Frank report explains the mechanism stating,
"Feed-in tariffs were introduced in the dying days of the Labour government and were designed to encourage people to create their own renewable electricity.
An index-linked payment guaranteed for up to 25 years is made for each unit of electricity produced even if it used by the generator for their own consumption. The tariff varies depending on how the energy is being generated and the scale of the scheme".
Although the hypothetical estate set out in the Rural Report gives the absolute optimal conditions for generating revenue from renewable energy, it nevertheless highlights the potential to make money though renewable energy. With project lifetimes of 25 years and revenues protected by government legislation, landowners are catching on to the fact that there is real money to be made from investing in renewable installations.
Kevin Langley is a leading knowledge in the Solar Investment and Renewable Energy world. Having worked with the subject for many years, he is fast becoming an expert on green energy and investments in green stocks.
He writes for many blogs and runs a range of Solar websites. He has a keen interest in green renewable energy and spends most of this writing time focusing on this subject.
Friday, December 17, 2010
We are now using our natural gas (carbonaceous fuel) resources up at a huge rate. These were formed from the fossilized remains of plants and animals in a process that took millions of years.
Such resources do not "grow back" in a time scale that is meaningful for humans. Natural gas is a fossil fuel that was created eons ago by the anaerobic decomposition of organic materials. It is often found in association with oil and coal. It will deplete without an adequate replacement other than biogas, so we had better get on with it and improve our ability to produce biogas and sngas (from gasification) - its only real replacement other than converting other carbonaceous fuels into gas fuels!
Cooking is best with with clean-burning gas, rather than smoky wood. Introducing gas cooking improves respiratory health and reduces the pressure on local fuelwood. In contrast, cooking on open fires emits gases that endanger people's health and contributes unnecessarily to global warming.
The German government saw the potential for biogas a number of years ago and introduced incentives to encourage biogas and biofuel production. German technology companies has a head start over the US, and the UK. Based on their experience, acquired over a number of years in partnership with their German customers, they have built a formidable record in biogas digestion.
The US should welcome these experts into the US. They do say that they want to share their expertise in other markets.
According to reports available on the internet they already have numerous projects and installations completed in Russia, Thailand, England, France, Spain and Turkey, and this they consider to be just the beginning.
It is stated in a recent report available on the worldwide web, that biogas even offers the possibility of stepping towards energy security for rural and even peri-urban communities in some areas. However, the converse is certainly true, and there is no energy security for any nation now in depending on imports of natural gas, whereas literally home-grown biogas is right on our doorstep, and as secure a supply as can be imagined.
There are two great sites where you can find out more about this developing alternative energy source and those are the electricity from methane digester web page and the biogas digestion web site. Take a look now!
Thursday, December 16, 2010
Methane is a combustible gas, which exists in two ways as part of the natural biological cycle when it is known as biogas, or biomethane, or as a mineral or fossil-fuel gas when it is called "natural gas".
As a mineral fuel it can be extracted from the earth's crust in the form of natural gas, or from waste sludge and biological sources including organic waste as biogas. Methane is widely accepted as the cleanest burning of all fossil fuels, but the extraction process itself requires careful consideration of the natural environment and local community.
Methane has been recently identified as a powerful greenhouse gas (GHG), and it has also been shown that its atmospheric concentration has been steadily increasing over the past 300 years. It is described as sustainable when it is produced by renewable energy (non mineral) sources, when it does not add to the GHG effect. All mineral sources are non-sustainable sources because they contribute to the GHG effect.
Methane is found trapped in air bubbles in ice cores, and measuring the quantity allows us to work out how much was present in the past. Studies of bubbles from the Greenland ice cap show that the concentration of methane in the air remained steady for 10,000 years, up until about 300 years ago.
If really large "burps" were released, quite substantial climatic changes would probably ensue. Methane is currently emitted in enough volume to make any reductions significant in terms of the overall GHG picture. Geochemical evidence for this process has been observed in numerous marine sediments along the continental margins, in methane seeps and vents, around methane hydrate deposits, and in anoxic waters.
There are two major ways in which methane is removed from the environment and these are aerobic oxidation by a specialized group of bacteria, and atmospheric oxidation.
Biogas /biomethane is produced by anaerobic oxidation by a specialized group of archaea, or methanogens.
Methane is emitted during the production and leaks from the distribution of natural gas and petroleum, and is released as a by-product of coal mining and incomplete fossil fuel combustion. Over many centuries as coal deposits are formed, some methane is absorbed by the coal and that is the usual source from which it is found in mines.
Biogas methane is released as vegetation rots under water. This is is happening in millions of square miles of rice fields throughout Asia.
It is combustible, and mixtures of about 5 to 15% in air are explosive. It is the main constituent of natural gas, a fossil fuel . Methane is far more lethal as a greenhouse gas - assuming that one believes in all this - than carbon dioxide. It is between 20 and 23 times more potent than Carbon Dioxide in terms of its GHG climate warming potential, depending upon how you look at its potency, although it does not last forever in the atmosphere.
Cows produce huge volumes of it. Contrary to what might be expected, organic cows produce less milk than conventionally farmed cattle, so their methane output per litre of milk tends to be much higher than the non-organic type.
When we say that methane is a much more potent greenhouse gas than CO2 we refer to the fact that eight for weight, it traps 21 times more heat energy. However, to get this in proportion methane is just one of six gases held responsible for global warming. Carbon dioxide is the second most abundant greenhouse gas behind water vapor.
There are huge quantities of methane in the permafrost. Permafrost in northern Siberia is reported to be 1,600 meters, (5,250 feet) thick and in in northern Alaska it is estimated at 650 meters (2,100 feet) thick Permafrost lies beneath about 80 percent of Alaska, and a higher percentage of Siberia. Permafrost on land, though, is as cold as -12.4 degrees Celsius.
Why do the GHG potencies vary so much between gases? Gases in the atmosphere, such as methane, absorb light energy and different gases absorb different amounts of energy.
Gas pipeline inspection is essential to maintain gas distribution systems, and minimize leakage, but it is a huge task. Just looking at the figures for Germany alone, with a network of more than 40,000 km of long-distance gas transport pipelines. Also, the need for a fast and remote monitoring system is apparent, to identify damage quickly.
Emissions from animal wastes depend on the method of storage or management of those wastes. When manure is stored as slurry, much of the decomposition is anaerobic and methane is produced in significant quantities. These emissions can and should be controlled by specific regulations.
Anaerobic digesters at local organic waste landfill sites or installed as part of large PFI systems capture and destroy the methane or clean it to comply with consumer standards. Large numbers of these plants installed throughout Europe would help to reverse the upward trend in methane discharges to the atmosphere. Nevertheless, even if large numbers of AD Plants were built rapidly, anaerobic methane oxidation will always remain biogeochemically important because methane is such a potent greenhouse gas in the atmosphere.
Tuesday, December 14, 2010
Anaerobic digestion is one of the methods through which biogas is produced. Biogas can be produced utilizing anaerobic digesters. Here, the plants can be fed with energy crops such as maize silage or biodegradable wastes including sewage sludge and food waste; whereas, the landfill gas is produced by organic waste decomposing under anaerobic conditions in a landfill. Gober Gas is the other form of biogas generated out of cow dung. This type of biogas is produced mainly in the households of India and Pakistan.
Biogas has many advantages over other alternative fuels. One of the main advantages of biogas is that the technology is cheaper and much simpler than those for other biofuels. Recovery of the methane is spontaneous as the gas automatically separates from the substrates. Dilute waste materials can be used as substrate. In the process of making biogas, organic pollutants are removed from the environment and used to generate useful biogas and this actually cleans the environment. Aseptic conditions are not needed for operation. Other advantage of biogas is that it will not produce any unpleasant odours. Electricity can be generated with biogas 24 hours a day. There is reduced risk of explosion as compared to pure methane and any biodegradable matter can be used as substrate for producing biogas.
As it has many advantages, biogas too has few disadvantages as well. One among them is that the product (biogas) value is rather low and this makes it an unattractive commercial activity. This process is not very attractive economically (as compared to other biofuels) on a large industrial scale. Biogas contains some gases as impurities, which are corrosive to the metal parts of internal combustion. Other major disadvantage of biogas is that its yields are lower due to the dilute nature of substrates.
Nevertheless, Biogas can become a great substitute for other conventional energy sources.
Clifton is a qualified mechanical engineer committed to finding alternative fuel sources that can be incorporated into everyday life.
Sunday, December 12, 2010
Yet, many farms are now going into Anaerobic Digestion plant installation and operation, investing in a process which is fairly new, at least for farming applications, and which they would expect to be operating on their farms for at least the next twenty years once installed. On the face of it this is a highly risky investment, and a surprise.
Well actually, there is good reason for this and it has very little to do with improving their crops, although the fertilizer it produces will be very useful there, it is to avoid environmental problems caused by the success of industrial farming methods, and particularly for dairy farmers who over-winter large numbers of stock in barns.
Let's not get too "down to earth" and talk about the brass tacks too much here, so shall we say that the problem is one of waste management, and leave as much as possible to your imagination!
Yes, the run-off from these barns and the effect this can have on pollution of rivers, in dairy farming and beef cattle rearing areas, can be and often is, very serious. So much enteric bacteria (stomach organism) type pollution has been occurring in in some estuarial areas of the UK that the quality of the sea on bathing beaches has failed to meet European Union Green Flag standards after heavy rainstorms.
These farms really have to reduce the pollutants in their run-off, and Anaerobic Digestion of their farm waste using a Biogas Digester is proving to be the top solution, once the problem is recognised. They are having to spend to reduce pollution because not cutting back massively on the quantities of organic waste being washed off their farms will increasingly mean that they will be prosecuted for the water pollution caused. Thus, this is a necessary spend for them, just to keep their farms operating on the right side of the law.
However, a biogas digester also can be used to generate renewable energy and provide fuel to run farm vehicles. So, many are finding it a great way to diversify away from solely food crop income dependence. In fact we would suggest that nowadays every farmer should be aware of the benefits of Anaerobic Digestion for its multiple benefits and great sustainability credentials.
Space is limited here so we recommend that you visit the Anaerobic Digestion community web site. It is well worth a visit for EVERYONE involved in a farm business. Much invaluable additional reading about the Biogas Digester's process, is available on that site.
Monday, December 06, 2010
RENEWABLE energy could be used in future to power Gloucestershire County Council’s buildings, to save money and cut carbon.
The innovative idea, being looked at by the Environment Scrutiny Task Group, could see the council saving £5m annually, generating income and becoming almost carbon neutral within 10 years.
In our video below we provide an example of a renewable energy biomass boiler in the London Borough of Havering. AD is another method which could be used.
Currently the council produces around 60,000 tonnes of carbon every year and spend more than £8million on energy bills.
The pioneering approach to renewables would make Gloucestershire one of the first councils in the UK to look at generating and selling our own electricity on this scale.
This will involve using green technology like solar panels, wind turbines and anaerobic digestion to become a lean, green council which provides all its own energy, reducing the financial burden on the council taxpayer.
At the moment there are no firm plans in place, but feasibility studies will be carried out over the next six months to determine what could be done.
One of the ideas is to set up a separate company to sell our surplus energy generated back to the grid, which will generate further income for the council.
The scrutiny group charged with looking into the issue was asked to investigate everything that we could achieve.
If GCC takes on all the ideas scrutiny have looked at, an estimated capital investment of £180 million would be needed to put all these ideas into place – but that would bring an annual return of £420 million.
To achieve the £5million savings and become carbon neutral would mean investments of around £25million, however no money has been committed to this project yet.
The council would also be eligible for funding from government if it decided to go down the renewable route and if the renewable plans are feasible they could generate additional incomes of around £14 million a year.
Cllr Mark Hawthorne, leader of the council, said: "This is not a quick fix, it’s about finding a sustainable way of working which dramatically cuts costs, reduces our impact on the environment and increases the security of energy supply.
"There is a cost involved here and before we commit to spending any money, we will ensure whatever we end up doing is worthwhile and will provide the benefits we expect.
"We have to invest now to save for the future and if we can save around £5 million every year and then make money on selling energy on top of that, this money can be ploughed into frontline services and that for me is the most important thing."
Cllr John Cordwell, who is the chair of the scrutiny committee looking into the project, said: "This group is looking into ways of saving money and investing into renewable energy by using council buildings and land.
"We are pleased to see the administration is of the same mind and we shall look forward to scrutinising the plans as they develop."
View the original article here
Friday, December 03, 2010
Lancashire-based Farmgen aims to build 50 environmentally-friendly anaerobic digestion power plants, which mimic the processes inside a cow's stomach to generate a methane-rich biogas.
The farm-based plants are fuelled by crops grown on site, and Farmgen has already agreed a deal to supply energy to Marks & Spencer.
The company is lead by Simon Rigby, former chief executive of the Leeds-based utilities infrastructure business Spice, which was sold to private equity outfit Cinven in September for £251m.
Farmgen's first plant at Carr Farm near Warton in Lancashire, which was formerly a dairy farm, is financed by a £2.1m loan from the Co-op, as well as funding from a group of private investors.
When fully operational next year it will generate 800kW of electricity – enough to power more than 1,000 homes.
Mr Rigby said: "It's a real lifeline for farmers and a big help for the UK economy. It gives farmers long term stability.
"It allows them to farm much more intensively, rather than just being subsistence farmers. It's going to breathe life into the countryside."
Farmgen was advised by a team from Manchester-based solicitors Heatons, which worked with the Co-op for nine months to secure the 11 year loan facility.
A team of six lawyers from the firm were involved in the project, advising on banking, corporate, construction, commercial and property matters.
Planning applications are currently being prepared for more plants across Lancashire, Cumbria and Staffordshire, with more sites being lined up across the country.
Partner James Flynn said: “This deal represented a new direction for the Co-operative but Farmgen’s plans for the plant are absolutely ground breaking.
“Farmgen’s overarching plan is to set up AD plants on farms across the UK. This could be a key driver in the country achieving its renewable energy targets, and we look forward to working with Farmgen on the future programme.
“For us, the energy sector is a big growth market for our business and so it is great to be involved in a project that is the first of its kind.”
View the original article here
Wednesday, December 01, 2010
The facility, at Lochhead Landfill Site near Dunfermline, is projected to generate up to 1.4 MW of renewable electricity and a similar quantity of heat from the processing of around 43,000 tonnes of co-mingled food and green waste.
SLR says that following two or three years of feasibility studies, it has been commissioned to undertake site investigation works, planning, permitting and procurement support for development of the facility which is projected to be operational by 2013.
Chris Ewing, environmental sstainability manager for Fife Council Environmental Services said: "The scheme represents a real opportunity for us to realise the true value from our expanding programme for source segregation of food and green wastes.
"The site already produces around 1.5MW of electricity through the combustion of landfill gas. The proposed development would nearly double the output of the site in addition to allowing for the expansion of the existing district heating scheme which utilises the excess heat from the CHP units."
SLR principal and project manager for the development Duncan Thomas, who is based in SLR's Edinburgh Office, said: "It is great to be assisting this long standing client in delivery of this ground-breaking project.
"We have been providing technical consultancy support to Fife Council for over seven years and continue to provide support on landfill engineering and development, permitting, planning, landscape and site investigation works."
View the original article here