A Memorandum of Understanding (MoU) was signed between Punjab government and a renowned Canadian Company High Mark Bio-Gas at Chief Minister’s Office on Friday for setting up bio-gas project. Chief Executive Officer Evan Chrapko on behalf of High Mark Biogas Company while Secretary Energy Usman Bajwa on behalf of Punjab government signed the MoU. According to the agreement, High Mark Bio-Gas Company will set up a pilot project of 22 megawatts of biomass gas in Punjab. The project will be completed within a short period of six months. Besides Chief Minister Punjab Muhammad Shahbaz Sharif, Provincial Energy Minister Sher Ali Khan, Chairman Planning and Development, Secretaries of Energy, Agriculture, Information, Local Government and other concerned officials were also present on the occasion. Sharif said signing of MoU between High Mark Bio-Gas Company and Punjab government with regard to biogas project was a welcoming step. He said vast opportunities of generating energy through bio-mass and biogas exist in Punjab and the provincial government will fully benefit from these opportunities. He said the experiences of foreign investors and companies would also be benefited in this regard so that energy crisis could be minimised at the earliest. The chief minister said besides traditional sources, Pakistan Muslim League-N government was also working for generating energy through non-traditional sources. He said non-traditional sources are the cheap source of generating energy which would provide relief to the people. Sharif said there was great potential of setting up bio-gas projects in Punjab and there was no shortage of fuel for the projects of biogas. He said energy crisis had made the life of common man miserable and the government was working on war footing for coping with this problem. The CM said Canadian Company will also carry out the process of mapping of waste used in biogas which will help in collecting authenticated data. Sharif said that after the success of first pilot project, new projects of biogas would be started. Earlier, Chief Executive of Canadian High Mark Bio-Gas Company, Evan Chrapko met Shahbaz Sharif at Chief Minister’s Office. Muhammad Umar Ghaznavi was also present on the occasion.
For the last five years, Ministry of Petroleum and Natural Resources (MPNR) has been trying to implement a LNG project of a rather small capacity of 400 Billion Cubic Feet per year (BCFD) and desperately tried to conclude an agreement in this respect in the last days of the reigning government of PPP. The LNG rates almost as much as that of oil (more than 80%) which it purports to replace, although there are some merits in that project. However, this is not the purpose of this article to delve into that. Similarly, Pakistan and Iran have both been trying to implement the IP gas pipeline project for years. Finally, the project was inaugurated on Iran side of the border without finalising the contract details and amidst vocal US opposition to the project and the murmur by opposition parties that it was a political inauguration designed to take undue credit and creating problems (of sanctions and US disgruntlement over the issue) for the next government. In this perspective, one would like to desperately search for other options including local production of gas. Biogas emerges as a good option, although not a complete replacement of the imported pipeline gas. It is intended in this article to explore the Biogas potential in Pakistan, its strength and weaknesses and evaluate various strategies to avail of its benefit. We will also explore in the end a rather interesting proposal; the prospects of using Biogas in CNG applications, something which CNG owners may love to read as the sector appears to be facing extinction in the wake of the gas crisis. Biogas is certainly not a new idea. The idea of producing Biogas for cooking has been on the cards for more than three decades in this country. In 1980s, attempts were made in the days of General Zia-ul-Haq to popularise Biogas. The initiative failed on account of many reasons detailing which may not be called for in this article. Several Rural development programme components are still there, which are dealing with Biogas for cooking with various degree of success or lack of it. Availability of cheaper and abundant gas and petrol resources has been one of the major reasons for underdevelopment of the alternative routes and products in the energy field. No more; neither the conventional sources are any cheaper any more and nor are these abundantly available. We have one-third of our power generation capacity under-utilised because we cannot afford to buy Fuel oil within the existing tariff framework, the latter being already too high and unaffordable for most consumers in the country. Pakistan a country of 200 million people and a large agriculture and a livestock sector (being the fourth largest milk producer in the world) produces a lot of Biomass and the associated waste. Animal dung, agri-waste, food and other Bio industry waste, Municipal Solid Waste (MSW) and sewerage could all generate valuable Biogas in addition to solving the perennial waste disposal problems. My estimates indicate that Pakistan has a potential of producing as much Biogas as it currently produces from its Gas Wells in Balochistan and Sindh, a whopping 1.6 TCF per year. Why the potential does remains unutilised? One may argue that nowhere in the world Biogas is a major source of energy. However, the situation is changing fast. Europeans have decided to generate Biogas to cater to the 20% of their gas requirement from Bio-sources by the year 2020 or so. While Americans are revelling in their Shale gas resource which is projected to last them for more than a century, Europeans produce only 40% of their gas requirements domestically and the rest is imported from Russia and the Middle East. In Europe a thriving and reliable gas market and network is operating based on local supplies and imports. Had their situation being as stark as ours, impetus on Biogas would have been even stronger. In any case, a 20% target is no mean a goal. Pakistan has a livestock population of over 50 million, which alone produces about 1 million ton per day of biomass (dung), most of which gets wasted producing local nuisance and global environmental problems (global warming due to methane release).This alone can generate 4 billion Cft per day, which is the shortfall that we are facing. Easier said than done? Obviously, all of the potential cannot be converted in gas and put into pipe lines. However, oil and gas demand can be reduced by generating and utilising biogas in many direct and indirect ways. Presently, small biogas plants are being installed for family needs in rural areas. The effort is continuing for the past many years. We have some 20 million rural house-holds. For 50% coverage, we require 5 million small biogas plants. This means, an installation activity of 500,000 biogas plants per year, if 50% target is to be achieved in 10 years. Due to poverty and capital needs, only a partial objective may be achieved in near future. Government subsidy and loan scheme can make a significant difference. The biggest merit of Biogas plants, especially the smaller ones, is that a lot of employment can be generated for the rural unemployed and landless workers. A reasonably sized Biogas programme say 100,000 plants per year can generate a direct employment of 50,000 workers not withstanding the stimulation of demand in cement and bricks sector. Finally, the motivation to shift from burning of Uplas and shrubs is lacking among the cash-starved rural poor. However, there is scope for commercial and industrial activity and investments in biogas sector. There are about one million agricultural Tube wells in Pakistan, 80% of which run on diesel. At Rs 100 a liter of diesel, the generators cost Rs 25 per unit of electricity generated. Farmers spend about 600-1000 Million USD worth of diesel annually to buy the required diesel to operate these tube wells. Farmers have started investing in Biogas plants that cost them Rs 0.5 million to run their generators. An equivalent solar tube well costs two to three times more. It is expected that wealthier ones would go for solar and less wealth would be installing Biogas plants. There are 30,000 large farms in Pakistan employing more than 50 cattle and 18000 farms rearing 200 cattle per farm on the average. Large Farms and cattle owners can produce electricity for others and sell it to the grid. A farm having 1000 cattle can generate 0.5 MW of electricity and a farm of 2000 cattle can generate 1 MW. One can reasonably assume that 1000 such farms can be marshaled to provide atleast 1000 MW, against a total potential of 3800 MW. Activity on this scale would require foreign technology and capital. Europeans would be keen to participate in this market, particularly Germany and Sweden where these technologies are thriving. A government policy would have to be evolved to facilitate all this. However, one is always scared of government policies which render every project expensive and unaffordable, the issue of costly Wind Power being a case in point. Wherever feasible, Biogas after cleaning and removing CO2 can also be fed into the gas network. Several such projects are being considered elsewhere and some are in operation as well. Recently, a Pakistani scientist settled in the US had prepared a proposal in this respect. I am not aware as to what happened. Concluding, in addition to centralized generation and networks, we should also look into distributed energy options. Most alternative energy technologies are suited for distributed mode except wind Power. Energy security and autonomy is enhanced by distributed applications. Centralized systems are too vulnerable to attack, terrorism and other threats and discontinuity. Biogas has a potential to meet our energy demands in a significant way while augmenting Energy security and self-reliance. PART-II : BIO-CNG-CNG FROM BIOGAS Bio-CNG is CNG produced from Bio sources instead of Natural Gas obtained from oil and gas fields. One could retrofit his CNG station with a Biogas plant and produce his own gas (Methane) instead of buying it from gas distribution companies such as SSGC and SNGPL. Raw material for the adjunct Biogas plant is to come from a variety of bio resources such as solid and liquid wastes and agricultural residues. In this article, we will explore the possibilities and role Bio-CNG can play in meeting the CNG demand in Pakistan. Factories are closed down due to non-availability of natural Gas. And there are long lines at CNG stations. CNG dealers criticise and even curse the Minister of Oil and Gas for their problems, but the fact is that there is an acute shortage of Gas. CNG dealers would also want to maintain a price differential of 50% between oil and gas prices in order to be able to maximise their revenues and profits. Even if LNG and Iran Gas Pipeline projects are implemented (a big if), gas prices are not going to be the same as these have been and still are. Both Iran and LNG suppliers are asking for very high rates, which is more than double our current rates. The morale of the story is to look for the other options and alternatives and develop these and stop living in the dream-world of cheap gas. This is a special message for the CNG dealers and their very vocal association. One would like to encourage them to Bio-CNG. As mentioned earlier, Biogas is nothing new, but Bio-CNG is and has come on the agenda only recently due to developments in technology and market. Biogas has 50% Methane and thus has to be upgraded, for use in automotives, to above 90% for technical and economic reasons. Also some gas cleaning is required to remove sulfur. This has been achieved successfully, technically and commercially only recently. One can now produce CNG at 50% of the price of Gasoline in the US Several commercial projects for self use by the producers have been launched. To reassure the skeptics, let me also reproduce the cuttings from a news-letter (Bio-Master) on the subject, which shows how active and popular the subject is in many countries: BIOGAS FROM SEWAGE TREATMENT PLANT TO POWER DELHI BUSES August 2012 Ambitious as it may sound, but Delhi plans to run its buses on biogas. In collaboration with the Swedish government, the Union Ministry of New and Renewable Energy plans to set up a biogas plant inside Kesopur Sewage Treatment Plant (STP) complex in West Delhi. INDIA TO TEST THE BIO-CNG PRODUCED FROM BAGASSE IN A COMMERCIAL VEHICLE February 2013 Under instructions from the Union Ministry for New and Renewable Energy (MNRE), Pune-based Automotive Research Association of India is expected to test the bio-CNG produced from bagasse and its use in operating a commercial vehicle. ENOC SIGNS AGREEMENT WITH DUBAI MUNICIPALITY TO PRODUCE CNG FROM WASTE FOR automotive use February 2013 Emirates Gas LLC (EMGAS), a subsidiary of Emirates National Oil Company (ENOC), has signed a Memorandum of Understanding with Dubai Municipality to treat land and sewage waste to generate compressed natural gas (CNG). EMGAS is now setting up an advanced facility to convert waste to bio-methane, from what is currently being flared, and then compress it into compressed natural gas that will be used as an automotive green. FIRST ECO-BUS ENTERS SERVICE IN ZALAEGERSZEG (HUNGARY) August 2012 The first eco-bus of the local public transport company entered service on 27 June. It is fuelled by biomethane, which is derived from the local sewage treatment plant. This action is part of a series of measures which aim to turn Zalaegerszeg into a sustainable town. TURKU AIMS TO USE MORE BIOGAS BUSES (FINLAND) October 2012 The city of Turku pledges to use the growing share of biogas to power its city buses. The aim is to make the bus transport within the city as environmentally friendly as possible. FIRST ECO-BUS ENTERS SERVICE IN ZALAEGERSZEG (HUNGARY) The first eco-bus of the local public transport company entered service on 27 June. It is fuelled by biomethane, which is derived from the local sewage treatment plant. This action is part of a series of measures which aim to turn Zalaegerszeg into a sustainable town. Ministry of Fuel (MFNRE) in India has approved about 15 projects subsidising up to 50% of the equipment cost of Bio-CNG installations. Local Government of New Delhi has decided to switch to Bio-CNG by producing Biogas from its solid waste facilities and get almost free fuel. Nothing is free though, the amortization costs and operating expenses would still yield a fuel cost saving of 50%. All public transport facilities and projects almost anywhere suffer from high cost issues not sufficiently covered under an affordable tariff. It is said that the newly established Metro-Bus project in Lahore also suffers from the same issue. However, Lahore generates a lot of solid and liquid waste and there should be ample agro-biomass around Lahore to be able to generate enough Bio-CNG at 50% of the Diesel prices. I hope the CM Punjab somehow reads it or get to know about it. Similarly, Karachi or for that matter all major cities can afford a public transport system under a cheaper and locally available fuel, in a country which calls itself an agricultural country. Reportedly, more than 35 CNG Buses procured by the local government of Karachi are in the docks, although for other than cost reasons. But improved economics and lesser fuel costs certainly help. Although, urban area CNG stations may not be able to benefit from Bio-CNG(except where local government develop projects from organic waste), CNG stations on the highways passing through rural areas can certainly install Bio-CNG facilities. A Bio-CNG plant consumes a lot of space for biogas generation plant, although the same compression facilities as are already available in conventional CNG would be required for compressing and filling Bio-CNG. In Punjab and Sindh, there should be a large number of existing CNG stations that could benefit from this concept. Capital investments of about Rs 10 Million have been estimated for installing Biogas facilities at the existing CNG pumps in rural areas. A wide variety of Biomass is available; Household and Municipal Solid waste , sewerage and waste water, agricultural, forestry and plant residue. To my knowledge, there is no single location or facility in Pakistan, where solid waste is hygienically and scientifically disposed off, except for some recycling activity self-sustained by commercial recyclers. In most countries particularly in Europe, hitherto, MSW had been incinerated, but now trend is changing towards gasification of solid waste. Waste heat was fed into heat exchangers to supply to the district heating systems or heat utilised in other applications. Incineration has become out of fashion due to environmental reasons as well. Increasingly solid waste is being disposed in Landfills which invariably produce Biogas. In Pakistan, a number of studies and efforts have been undertaken in the past to generate electricity from Municipal Solid Waste (MSW), but could not succeed due to a variety of reasons including poor economics and comparatively lower Calorific value of Pakistani MSW. Most, in fact all cities throw their MSW in uncovered waste dumps spreading squalor and disease in adjoining areas. Often, it is shamefully and carelessly burnt in the open very close to the residential areas. Any body who has crossed the Korangi bypass at night would know how dangerous this activity is. Bio-gasification and Bio-CNG may improve the economics of collection and disposal of MSW in most communities, especially major cities. Villages and Rural Centers can replace diesel from their diesel engines of the tube wells. Also, tractors could be switched to Bio-CNG. Where Biomass should be used for producing electricity or where it should be used for Biogas for cooking or for Bio-CNG, would depend on time and space issues and choices of the stakeholders. No policy can be announced promoting or proscribing a certain use, although it is clear that in case of Bio-CNG, the alternative or opportunity cost is much higher, ie Bio-CNG is replacing expensive gasoline and diesel, while there are cheaper options to produce electricity than from Biomass. Enterprise and innovation is augmented by the economics. A textile entrepreneur in Punjab is reportedly buying several hundred Buffaloes (which in addition to Milk) to provide Gober fuel which would generate Biogas which in turn would be used in electricity generation for his adjacent Textile Mill. The Gober generated Biogas would also be burnt in their Boilers. Certainly, Bio-CNG would not be a panacea for our energy problems or a one-size-fit-all solution. Cheaper Oil and gas used to be such a panacea and a solution, but no more. But one could expect that a significant portion of CNG demand could be met through Bio-CNG. Localised and segmentised solutions for a variety of users and market conditions may have to be implemented by the private sector mostly, although Government can guide, facilitate and afford some demonstration and early project subsidies. These kinds of solutions such as Bio-CNG, apart from being economic and affordable, also add to our energy security. Imagine what would happen, if oil import facilities or market suffer some kind of blockade or discontinuity, or the law and order problem, affecting the inter-city transport. Biogas is locally produced as would be Bio-CNG. Concluding, Bio-CNG appears to be an interesting and viable alternative to conventional CNG. Bio CNG should be allowed to grow in an unhindered market environment. Except for quality and safety issues, there should be no regulation, of price or otherwise. It should be the individual CNG dealer's choice weather and where he should invest to produce and sell CNG. However, a government policy would be required to reassure potential investors and the existing CNG dealers that their investment and efforts would not be wasted and that at some point in time, government may start discouraging out. No policy is for ever. Circumstances keep changing and new challenges and issues are to be handled. However, sufficient time and opportunity should be made available before a change of policy stance to enable the investors to recoup their investments. Fortunately, in the case of Bio-CNG, Bio-gasification facility would always have many other alternative markets and usages. Bio-CNG should be allowed to grow in an uncontrolled market environment. Except for quality and safety issues, there should be no regulation, of price or otherwise. It should be the individual CNG dealer's choice weather and where he should invest to produce and sell CNG.
Table: Biogas Potential in Pakistan
====================================================
No of Livestock=56.9 Million
Live stock Biomass generation=1 Mn Tons/day
Number of Large Dairy Farms=30,000 (avg 200 Cattles)
MSW =55000 tons/day
Crop residue= 225000 tons/day
Annual Biogas (Bio-methane) potential=1.6 TCF/yr
Pakistan Ngas Production=1.4 TCF/yr
Existing Short Fall= 1 TCF/yr
CNG consumption=0.164 TCF/yr
LNG projects =0.146 TCF/yr (25 Billion USD imports)
OR Electricity Potential from Biogas =3800 MW
----------------------------------------------------
Source: Author's Estimates
=============================
DAIRY FARM HERD SIZE AND BIOGAS & ELECTRICITY OUTPUT
========================================================
No of animals Gas out put Tot.Gas Tot.Electr Power Profit
number CM/animal/d Mbtu/yr kWh/yr KW Rs/yr
========================================================
5000 2.4 147000 14700000 2940 14700000
3000 2.4 88200 8820000 1764 8820000
2000 2.4 58800 5880000 1176 5880000
1000 2.4 29400 2940000 588 2940000
500 2.4 14700 1470000 294 1470000
200 2.4 5880 588000 117.6 588000
======================================================
Source: http://www.brecorder.com
What is Biogas? Biogas is naturally produced when any organic matter decomposes under anaerobic conditions (in the absence of oxygen).
The gas consists mainly of methane (CH4) and carbon dioxide (CO2) in approximately 3:2 ratio.
Methane is the important component, as it is a highly flammable gas that can be utilized as fuel for cooking, lighting, water heaters and, if the sulphur is removed, it can be used to run biogas-fuelled generators to produce electricity.
Biogas can be produced under controlled circumstances in specially designed biogas digesters.
There are many types of digesters that are being used throughout the world. In countries such as Germany, biogas technology is highly advanced and applied primarily to produce green electricity in the megawatt range. In other developing countries such as India and China, a more basic technology is used to provide energy primarily for cooking purposes. India for instance, has more than a million digesters producing all the cooking energy for thousands of villages using human (sewerage) and animal (manure) waste in the process. One of the major spin-offs of using a biogas digester, is that the spent material is in the form of organic compost that can then be used to increase the yield of planted crops.
The Benefits of Biogas The use of biogas is practically limitless. As a combined sewerage management/biogas producing system, any new house, guest house, lodge, development, golf estate, clinic, hotel, etc. can install a biogas digester system. It can be their primary sewerage system, or a source of alternative and sustainable energy in the form of biogas. The digestate can be applied directly as organic compost, or the water can be recycled through a wetland. Commercially biogas digester systems can be installed at dairies, piggeries, chicken farms, abbotoirs or any other type of industry where waste containing organic material is produced, to generate green sustainable electricity. A biogas digester has the following advantages: It produces methane gas that can be used for cooking purposes, lighting, water heating and to generate electricity It digests organic waste (from the kitchen, garden, sewerage, animal manure, etc.) It prevents methane gas from entering the atmosphere (methane gas is 20 times more harmful to the environment than CO2) It produces organic compost as waste product (in liquid, slurry or solid form) Who Can Use Biogas?
SMALLHOLDINGS: The ideal application for the Puxin Family Size Digester (10m3 digester) is for smallholdings, especially if there is some access to animal manure. Adding animal manure over and above the household sewerage, greatly increases the production of methane gas. Practical use of the gas is primarily for cooking purposes, but the gas can also be used in the Puxin biogas water heater, biogas lights and to generate (standby) electricity by using a biogas generator. LARGER SETUPS: The next market segment is for larger setups such as guest houses, schools, clinics, or small farms where multiple units of the 10m3 digester are used. Sizing of the system is directly proportional to the amount of material fed into the digester, whether the system is designed primarily as a sewerage system or for the production of biogas. The amount of methane produced is dependent on the amount of gas producing material fed into the digester, limited to an approximate maximum of 5m3 of gas per 10m³ digester per day. COMMERCIAL FARMING CONCERNS: Dairies, pig farms and chicken farms that produce large quantities of manure fall into this category. Implementing a biogas digester system for these concerns could potentially be of enormous financial benefit for such ventures. Under normal circumstances the huge amounts of manure produced is more of a liability than an asset and either gets dumped or sold to composting companies for a nominal fee. By installing a biogas digester system, the manure now becomes a major asset, able to produce practically free energy. This energy in the form of biogas can now be utilized to generate electricity, heat water, provide lighting or could be used for cooking purposes by the personnel on site. For this type of application Biogas SA will install their large 100m3 Puxin digester in conjunction with multiple gas holders. Biogas SA can supply and commission any size of biogas generator from a small 5kVA to very large 500kVA unit, depending on client's requirements. MUNICIPAL SEWERAGE WORKS: The Puxin technology is ideally suited to design and construct major sewerage works. Biogas technology can be used to replace existing technology and practices at our municipal sewerage works, not only providing a better way to deal with raw sewerage, but providing free energy in the process. Due to various reasons, a large number of our municipal sewerage works have become inefficient, is starting to cause serious pollution problems and is contributing to large scale contaminations of our precious water resources in South Africa. Commissioning biogas systems to replace the failing sewerage works has the potential to change this potentially disastrous situation into a win-win situation for all parties concerned. The cost of such biogas installations could be offset by claiming international carbon credits, the biogas generated could be used to generate electricity that could either be sold back to the grid or be used locally and the spent slurry could be sold off as organic compost. The major advantage to the environment is that the eventual effluent produced, will be of such a standard that it could in actual fact improve the quality of the water of the rivers it gets pumped into! Biogas SA with its association with The Shenzhen Puxin Science and Technology Company of China, is in a position to provide the full spectrum from design to implementation of fully functional, technologically advanced, biogas digester systems for the management of large scale sewerage works. This is applicable not only for municipal sewerage works, but also for any large scale residential developments, housing estates, golf estate developments, etc. PUBLIC SECTOR INSTITUTIONS:
Biogas SA can provide a service to all kinds/levels of public sector institutions such as schools, clinics, national parks, etc. and can be particularly effective if we could get involved during the design stage of such projects. It is a lot more cost effective to incorporate a biogas digester as part of the initial design, rather than doing a retro-fit at a later stage. WASTE RECYCLING PLANTS: Any form of organic waste can be used as fuel for a biogas digester to produce methane. This introduces a whole new market not previously addressed by traditional digesters due to the difficulty of removing the solid spent waste from the digester. The Puxin digester has a large fiberglass reinforced dome that can easily be removed (no danger of trapped gas), giving easy access to clean the digester out and re-load with fresh material. This means that any type of organic waste material generated such as agricultural waste, restaurant/hotel food waste, municipal garden waste, waste from fresh produce markets, abattoir waste and any other waste one can think of as long as it is organic in nature. It can potentially be a solution to the water hyacinth problem! Tapping into free energy in the form of methane gas by feeding organic waste into a biogas digester is one of the most practical and cost effective ways to generate alternative, sustainable and environmentally friendly energy for all in South Africa.
What Do We Use To Produce Biogas? THE PUXIN DIGESTER: Biogas SA is the sole licensee for South Africa of the Shenzhen Puxin Science and Technology Company (Puxin) of China. Puxin has developed over a period of 20 years a unique, patented hydraulic biogas digester that has eliminated all the disadvantages and enhanced the advantages of the more traditional fixed and floating dome type digester designs. As acknowledgement of its technology and contribution to promoting efficient alternative energy resources, Puxin was awarded the prestigious Global Top Ten Investment Scenarios to Apply New Technologies for Renewable Energy Utilization BlueSky Award in 2006, initiated by the United Nations Industrial Development Organisation. The Puxin digester basically consists of a belly, a neck, the plastic gas holder or dome, an inlet and an outlet. One of the main features of the digester is the fact that it basically functions as a hydraulic system. The entire digester is flooded with water, with the water at the same level in the inlet, digester neck and outlet. The fact the decomposition of the material now takes place under water, creates the ideal anaerobic conditions so critical for the creation of methane gas. The added advantage of the water is that it is also responsible for creating the constant pressure under which the biogas is available in this type of digester. As the biogas is produced in the bottom of the digester belly, it rises upwards and is eventually caught in the dome. As the volume of gas increases, it starts to replace the water in a downward direction. The resulting upward pressure of the replaced water ensures that the collected biogas in the dome is always under constant pressure (up to 8 bar). The fact that the gas is always available at the same constant pressure is a major advantage for the efficient running of most gas appliances. It is practically impossible to run a generator for instance, if the gas feeding the generator is not available under constant pressure; the generator will simply cut out every time the pressure drops. Another advantage of the Puxin design, is the ease with which the digester can be emptied out. Because it is so easy to clean, any type of organic material can be used as feeder material. Where it is not practical to empty a digester (fixed dome type), only material such as manure that leaves now solid residuals after the decomposition process is complete, can be used as feeder material. Organic waste such as leaves, straw, grass, etc do not decompose to the same extent as manure and will always leave solid waste after decomposition. This spent material needs to be removed from the digester before the digester can be reloaded with new material. The light weight Puxin digester dome can easily be removed by two people, making it a practical system suitable to use organic waste as feeder material. This is a major advantage for applications where manure is not available in the necessary quantities, but enough organic material is available.
