Renewable Energy in Refugee Camps

Access to clean, affordable and renewable energy is a prerequisite for sustainable development of mankind, and refugees are no exception. Refugee camps across the world house more than 65 million people, and almost all refugee camps are plagued by fuel poverty. Needless to say, urgent measure are required to make camps livable and sustainable.

dabaab-refugee-camp

Rapid advancements in renewable energy technologies have made it possible to deploy such systems on various scales.  The scalability potential of renewable energy systems makes them well-suited for refugee camps, especially in conflict-afflicted areas of the Middle East, Asia and Africa.

Renewable energy in refugee camps can be made available in the form of solar energy, biomass energy and wind energy. Solar panels, solar cooking units, solar lanterns, biomass cookstoves and biogas plants are some of the popular renewable energy technologies that can improve living standards in refugee camps. It is important to focus on specific needs of refugees and customization of technology towards local conditions. For example, solar technologies are better understood than biogas systems in Jordan.

Solar Energy

Solar energy can provide long-term resilience to people living in refugee camps. With many camps effectively transformed into full-fledged towns and cities, it is essential to harness the power of sun to run these camps smoothly. Solar cookers, solar lanterns and solar water heaters are already being used in several refugee camps, and focus has now shifted to grid-connected solar power projects.

The 5MW Azraq solar project is the world’s first grid-connected renewable energy project to be established in a refugee camp. The project is being funded entirely by Ikea through the Brighter Lives for Refugees campaign. The program, now in its third year, seeks to improve the lives of refugees around the world by providing access to sustainable energy supplies.

Biomass Energy

Due to lack of land and resources, refugee camps puts tremendous pressure on natural vegetation, especially supply of fuel wood to camp-dwellers. Replacement of traditional stoves with efficient biomass-fired cook stoves can save as much as 80% of cooking fuel.

Instead of wood, it would be also be a good option to use agricultural wastes, like husk and straw. Another interesting proposition for refugee camps is to set up small-scale DIY biogas plants, based on human wastes and food residuals. The biogas produced can be used as a cooking medium as well as for power/heat generation.

Wind Energy

Small wind turbines can also play a key role in providing energy to dwellers of refugee camps. Such turbines are used for micro-generation and can provide power from 1kW to 300kW. Majority of small wind turbines are traditional horizontal axis wind turbines but vertical axis wind turbines are a growing type of wind turbine in the small wind market. Small wind turbines are usually mounted on a tower to raise them above any nearby obstacles, and can sited in refugee camps experiencing wind speeds of 4m/s or more.

Solar lights in Azraq Refugee Camp (Jordan)

Solar lights in Azraq Refugee Camp (Jordan)

Conclusions

Renewable energy systems have the potential to improve living standards in refugee camps and ease the sufferings of displaced and impoverished communities. Solar panels, biogas system, biomass stoves and micro wind turbines are some of the renewable energy systems that can be customized for refugee camps and transform them into a less harsh place for displaced people.

Weather-Resistant Building Materials for 2020

Homeowners are always wary of extreme weather conditions such as flooding, severe rain, excess heat, and extreme coastal surges. Extreme weather can either damage the exteriors of a home or make the indoor temperatures too hot or too cold to bear. That leads to expensive repairs or high costs of energy. To protect a home from extreme weather, the best thing to do is build using water-resistant materials and to elevate your house in a way that surging floods don’t sweep your house away. If you have resolved to build a new home in 2020, here are some of the most weather-tolerant materials to consider:

1. Concrete

Concrete is one of the strongest building materials out there, particularly when it comes to withstanding pressure and stress. This material can be pre-casted to become water-resistant, it doesn’t expand or contract in extreme weather, and when reinforced with rebar and pre-stressed, it can be extremely durable. What’s more, concrete is readily available all over the world at very affordable prices. You can use it to build your basement walls or a slab foundation for your home or rental property by hiring services of specialized companies.

2. Wood

Wood is one of the oldest building materials. I mean, it was used to build shelters in the mid-stone age. You can use wood as a primary siding material or reinforce it with concrete or metal to make it stronger and more durable. Wood is also a bad conductor of heat, making it an ideal material to use in areas that experience extremely hot or extremely cold seasons.

However, wood has one key disadvantage: It can decay when exposed to excess water for a prolonged period. It can withstand moderate moisture for a decade or two especially when there is an occasional sun to dry it up, but it will eventually decay. The positive thing is that wood can be painted and treated to prevent it against moisture damages.

3. Vinyl

Vinyl is a great siding installation due to its ability to shed rainwater away. It is not 100% water-resistant, but it has superior water resistance than wood. In most cases, vinyl is installed in a standard interlocking horizontal wall, so it does not retain much dampness or snow after a rainy season. Modern vinyl panels are made with “weep holes” that aid in channeling away excess water in order to keep the siding wall dry at all times, consequently increasing its durability.

You can also reinforce it with an insulation board so as to keep away any stubborn moisture that refuses to dry away through the weep holes. A house wrap is also a great secondary reinforcement- it ensures that moisture doesn’t penetrate the sidings, consequently keeping your interiors warmer than the exteriors.

4. Metal roofing

For the homeowners who live in hailstone-prone areas, metallic hail-resistant roofing shingles are your best bet. Such roofing will withstand storm damage and remain intact even when high winds blow through your region. If you want a hail-resistant roofing option that is also stylish and contemporary, you can try the stone-coated metal roofing tiles.

5. Fire-resistant materials

There are areas that are more prone to fire outbreaks than storm damages. California, for example, experience lots of wildfires during summer months than they experience storms during winter. If you live in such an area, then you need to use building materials that make your home as fire-resistant as possible. Sometimes it is hard to avoid these acts of nature, but your contractor can help you mitigate their effects.

You can, for example, install fire-rated roofing that resists ignition even when exposed to extremely high temperatures. There are also windows that don’t shatter in heat. Even if these materials won’t be salvaged after the fire, they will at least prevent your interiors from the fire. You will only need to do minor rehabilitations to your home’s exteriors once the fire subsides.

6. Stone

Most ancient buildings world over are made of stone. This material is durable and can withstand almost every extreme weather condition you can think of. It is also classy and readily available.

Conclusion

There are many weather-resistant materials to check out in 2020. More new materials will be invented going forward, and the existing ones will continue being reinforced in order to increase their durability and strength. The six materials discussed above will get the job done. If you need more, make sure you research widely and talk to as many homeowners in your area before settling for a material.

Waste to Energy Conversion Routes

Waste-to-energy is the use of modern combustion and biological technologies to recover energy from urban wastes. There are three major waste to energy conversion routes – thermochemical, biochemical and physico-chemical. Thermochemical conversion, characterized by higher temperature and conversion rates, is best suited for lower moisture feedstock and is generally less selective for products. On the other hand, biochemical technologies are more suitable for wet wastes which are rich in organic matter.

Teesside-WTE-plant

Thermochemical Conversion

The three principal methods of thermochemical conversion are combustion in excess air, gasification in reduced air, and pyrolysis in the absence of air. The most common technique for producing both heat and electrical energy from household wastes is direct combustion.

Combined heat and power (CHP) or cogeneration systems, ranging from small-scale technology to large grid-connected facilities, provide significantly higher efficiencies than systems that only generate electricity.

WTE_Pathways

Combustion technology is the controlled combustion of waste with the recovery of heat to produce steam which in turn produces power through steam turbines. Pyrolysis and gasification represent refined thermal treatment methods as alternatives to incineration and are characterized by the transformation of the waste into product gas as energy carrier for later combustion in, for example, a boiler or a gas engine. Plasma gasification, which takes place at extremely high temperature, is also hogging limelight nowadays.

Biochemical Conversion

Biochemical processes, like anaerobic digestion, can also produce clean energy in the form of biogas which can be converted to power and heat using a gas engine. Anaerobic digestion is the natural biological process which stabilizes organic waste in the absence of air and transforms it into biofertilizer and biogas.

Anaerobic digestion is a reliable technology for the treatment of wet, organic waste.  Organic waste from various sources is biochemically degraded in highly controlled, oxygen-free conditions circumstances resulting in the production of biogas which can be used to produce both electricity and heat.

In addition, a variety of fuels can be produced from waste resources including liquid fuels, such as ethanol, methanol, biodiesel, Fischer-Tropsch diesel, and gaseous fuels, such as hydrogen and methane. The resource base for biofuel production is composed of a wide variety of forestry and agricultural resources, industrial processing residues, and municipal solid and urban wood residues. Globally, biofuels are most commonly used to power vehicles, heat homes, and for cooking.

Physico-chemical Conversion

The physico-chemical technology involves various processes to improve physical and chemical properties of solid waste. The combustible fraction of the waste is converted into high-energy fuel pellets which may be used in steam generation. The waste is first dried to bring down the high moisture levels. Sand, grit, and other incombustible matter are then mechanically separated before the waste is compacted and converted into fuel pellets or RDF.

Fuel pellets have several distinct advantages over coal and wood because it is cleaner, free from incombustibles, has lower ash and moisture contents, is of uniform size, cost-effective, and eco-friendly.

Overview of Biomass Energy Systems

Biomass is a versatile energy source that can be used for production of heat, power, transport fuels and biomaterials, apart from making a significant contribution to climate change mitigation. Currently, biomass-driven combined heat and power, co-firing, and combustion plants provide reliable, efficient, and clean power and heat.

Feedstock for biomass energy plants can include residues from agriculture, forestry, wood processing, and food processing industries, municipal solid wastes, industrial wastes and biomass produced from degraded and marginal lands.

The terms biomass energy, bioenergy and biofuels cover any energy products derived from plant or animal or organic material. The increasing interest in biomass energy and biofuels has been the result of the following associated benefits:

  • Potential to reduce GHG emissions.
  • Energy security benefits.
  • Substitution for diminishing global oil supplies.
  • Potential impacts on waste management strategy.
  • Capacity to convert a wide variety of wastes into clean energy.
  • Technological advancement in thermal and biochemical processes for waste-to-energy transformation.

Biomass can play the pivotal role in production of carbon-neutral fuels of high quality as well as providing feedstock for various industries. This is a unique property of biomass compared to other renewable energies and which makes biomass a prime alternative to the use of fossil fuels. Performance of biomass-based systems for heat and power generation has been already proved in many situations on commercial as well as domestic scales.

Biomass energy systems have the potential to address many environmental issues, especially global warming and greenhouse gases emissions, and foster sustainable development among poor communities. Biomass fuel sources are readily available in rural and urban areas of all countries. Biomass-based industries can provide appreciable employment opportunities and promote biomass re-growth through sustainable land management practices.

The negative aspects of traditional biomass utilization in developing countries can be mitigated by promotion of modern waste-to-energy technologies which provide solid, liquid and gaseous fuels as well as electricity as shown. Biomass wastes can be transformed into clean and efficient energy by biochemical as well as thermochemical technologies.

The most common technique for producing both heat and electrical energy from biomass wastes is direct combustion. Thermal efficiencies as high as 80 – 90% can be achieved by advanced gasification technology with greatly reduced atmospheric emissions. Combined heat and power (CHP) systems, ranging from small-scale technology to large grid-connected facilities, provide significantly higher efficiencies than systems that only generate electricity.  Biochemical processes, like anaerobic digestion and sanitary landfills, can also produce clean energy in the form of biogas and producer gas which can be converted to power and heat using a gas engine.

In addition, biomass wastes can also yield liquid fuels, such as cellulosic ethanol, which can be used to replace petroleum-based fuels. Cellulosic ethanol can be produced from grasses, wood chips and agricultural residues by biochemical route using heat, pressure, chemicals and enzymes to unlock the sugars in lignocellulosic biomass. Algal biomass is also emerging as a good source of energy because it can serve as natural source of oil, which conventional refineries can transform into jet fuel or diesel fuel.

4 Hacks to Make Your Next Home Greener

There is a huge spotlight on the construction industry when it comes to green initiatives – and rightly so. After all, this is one of the biggest contributors to all of the sustainable problems that the world faces. However, this increased focus does prompt some problems. It can make some people believe that going green in the home is out of the question – and is only going to be achieved through some really costly implementations.

Granted, there are some major infrastructure projects you can invest in if you are building a home, with solar power and ground source heat pumps tending to grab the headlines. At the same time, there are smaller wins – and these shouldn’t be underestimated, such as solid wood flooring. In fact, if everyone was to invest in these, we’d suggest that the typical carbon footprint across cities such as San Diego would drop substantially.

Taking this into account, let’s now take a look at some of the quick, green wins you can succeed with as you bid to make your next home more sustainable.

It starts with the placement of your windows

As we work with our architect in the initial design phase of our project, many of us are more concerned about the size of our bedrooms and so on.

A common afterthought is the placement of windows. Sure, some people might think about this as they consider natural light implications – but it’s time to think bigger.

Let’s not forget that as well as allowing rooms to heat naturally, windows are something that lets warm air escape. It means that their position is crucial, and treating them as an afterthought is asking for a completely inefficient dwelling.

Never forget insulation

In some ways, we were almost tempted not to include this next point. After all, insulation is an old classic when it comes to energy efficiency. It is something that has been suggested for years, mainly because it is incredibly cheap to implement whilst also being very effective.

Of course, it’s always easier to install insulation during the early phases of a project. Try and remember to focus on the roof and walls; this is where most of your heat is lost and is where you can make the biggest difference.

It’s not just about energy; think water as well

A lot of today’s guide has looked at energy, and rightly so. We are also going to dip into a point about water consumption, though.

This is something that often gets forgotten about, but the benefits are substantial. A lot of older, traditional bathroom fittings are anything but efficient – they deliver water at a ridiculous rate, and ultimately waste it.

If you turn to modern-day solutions, you’ll find that you can save gallons every year. Suffice to say, this isn’t just going to benefit your environment, but your pocket as well.

Your roof is crucial

Finally, if there was just one area of your next home to concentrate on, your roof should be up there as a priority. Nowadays, there are all sorts of materials that can help your plight. For example, for those of you who reside in hot countries, you can turn to roofs with reflective paint to deal with the heat somewhat. Green roofs are another solution which are surging in popularity but in truth, the list could go on.

Recommended Green Resources:

Biomass Cogeneration Systems

Biomass fuels are typically used most efficiently and beneficially when generating both power and heat through biomass cogeneration systems (also known as combined heat and power or CHP system). Biomass conversion technologies transform a variety of wastes into heat, electricity and biofuels by employing a host of strategies. Conversion routes are generally thermochemical or biochemical, but may also include chemical and physical.

The simplest way is to burn the biomass in a furnace, exploiting the heat generated to produce steam in a boiler, which is then used to drive a steam turbine. Advanced biomass conversion technologies include biomass integrated gasification combined cycle (BIGCC) systems, cofiring (with coal or gas), pyrolysis and second generation biofuels.

Biomass Cogeneration Systems

A typical biomass cogeneration (or biomass cogen) system provides:

  • Distributed generation of electrical and/or mechanical power.
  • Waste-heat recovery for heating, cooling, or process applications.
  • Seamless system integration for a variety of technologies, thermal applications, and fuel types into existing building infrastructure.

Biomass cogeneration systems consist of a number of individual components—prime mover (heat engine), generator, heat recovery, and electrical interconnection—configured into an integrated whole. The type of equipment that drives the overall system (i.e., the prime mover) typically identifies the CHP unit.

Prime Movers

Prime movers for biomass cogeneration units include reciprocating engines, combustion or gas turbines, steam turbines, microturbines, and fuel cells. These prime movers are capable of burning a variety of fuels, including natural gas, coal, oil, and alternative fuels to produce shaft power or mechanical energy.

Key Components

A biomass-fueled cogeneration facility is an integrated power system comprised of three major components:

  • Biomass receiving and feedstock preparation.
  • Energy conversion – Conversion of the biomass into steam for direct combustion systems or into biogas for the gasification systems.
  • Power and heat production – Conversion of the steam or syngas or biogas into electric power and process steam or hot water

Feedstock for Biomass Cogeneration Plants

The lowest cost forms of biomass for cogeneration plants are residues. Residues are the organic byproducts of food, fiber, and forest production, such as sawdust, rice husks, wheat straw, corn stalks, and sugarcane bagasse. Forest residues and wood wastes represent a large potential resource for energy production and include forest residues, forest thinnings, and primary mill residues.

combined-heat-and-power

Energy crops are perennial grasses and trees grown through traditional agricultural practices that are produced primarily to be used as feedstocks for energy generation, e.g. hybrid poplars, hybrid willows, and switchgrass. Animal manure can be digested anaerobically to produce biogas in large agricultural farms and dairies.

To turn a biomass resource into productive heat and/or electricity requires a number of steps and considerations, most notably evaluating the availability of suitable biomass resources; determining the economics of collection, storage, and transportation; and evaluating available technology options for converting biomass into useful heat or electricity.

How Solar Roofs Can Minimize The Urban Heat Island Effect

As cities grow, open spaces, trees and other greenery, and other naturally occurring surfaces diminish, replaced by concrete and asphalt surfaces. When this happens, the heat absorbed by these surfaces has nowhere to go, and so is radiated and reflected into the immediate surrounding areas. This creates an urban heat island.

This leads to an increase in heat in the immediately surrounding areas, making temperatures a few degrees hotter than the actual weather. This causes discomfort to residents of the area and can also incur damage in the form of heat-damaged structures.

There is also a human cost associated with urban heat islands. Heat-related medical emergencies such as heat stroke become more prevalent in such areas as the heat can go up to dangerous levels. The EPA has taken stock of this phenomenon and is now advising cities to take steps to mitigate it. One such way is the use of Los Angeles solar as a means of making cities cooler and more comfortable to live in.

How does solar minimize this effect?

Cool Roof Strategy

A cool roof strategy is a one that seeks to use heat absorbing and/or dissipating roofing materials and technologies. Typical roofs use materials that either reflect or absorb and radiate back heat thus significantly reducing the urban heat island effect. Conversely, cool roofs, like solar, can help absorb sun rays and convert them into beneficial energy.

Solar excels at this because of the way the cells are designed and organized to absorb the maximum amount of sunlight. Solar roofs are also designed to trap this heat rather than radiate it back into the environment, something that can help reduce the amount of secondary heat being released into the environment.

Reduced Construction

When solar roofs are implemented, there is usually a reduced need to construct structures that support the traditional electric grid. Such a scenario can play out in several ways. If a new estate is being built with nothing but solar power, there is a possibility that some open spaces can be retained as fallow ground in places where utility implements would have been installed.

While the gains at this level would be marginal, implementation of this strategy across several thousand estates can help move the needle in reducing the urban heat island effect.

Combination Approach

This approach offers the greatest promise of reducing heat in urban settings. By combining the cool roof strategy with other strategies like green roofing, planting more trees and vegetation, cool paving and general smart city growth, a lot of ground can be covered.

Planting more trees and vegetation will go a long way in reducing heat in urban settings.

All these strategies have one thing in common in that they all absorb and dissipate heat in an efficient and sustainable manner. The EPA recommends these measures, among others, to cities grappling with the urban heat island effect or anticipating it as open spaces and greenery levels go down.

Many cities have a high incentive to deal with this issue because of its effect on residents and visitors to the area. If street-level temperatures are unbearable, it is possible that tourists and potential new residents may shy away from the area in favor of other cooler cities.

Pyrolysis of Municipal Wastes

Pyrolysis is rapidly developing biomass thermal conversion technology and has been garnering much attention worldwide due to its high efficiency and good eco-friendly performance characteristics. Pyrolysis technology provides an opportunity for the conversion of municipal solid wastes, agricultural residues, scrap tires, non-recyclable plastics etc into clean energy. It offers an attractive way of converting urban wastes into products which can be effectively used for the production of heat, electricity and chemicals.

Pyrolysis-MSW

Pyrolysis of Municipal Wastes

Pyrolysis process consists of both simultaneous and successive reactions when carbon-rich organic material is heated in a non-reactive atmosphere. Simply speaking, pyrolysis is the thermal degradation of organic materials in the absence of oxygen. Thermal decomposition of organic components in the waste stream starts at 350°C–550°C and goes up to 700°C–800°C in the absence of air/oxygen.

Pyrolysis of municipal wastes begins with mechanical preparation and separation of glass, metals and inert materials prior to processing the remaining waste in a pyrolysis reactor. The commonly used pyrolysis reactors are rotary kilns, rotary hearth furnaces, and fluidized bed furnaces. The process requires an external heat source to maintain the high temperature required.

Pyrolysis can be performed at relatively small-scale which may help in reducing transport and handling costs.  In pyrolysis of MSW, heat transfer is a critical area as the process is endothermic and sufficient heat transfer surface has to be provided to meet process heat requirements.

The main products obtained from pyrolysis of municipal wastes are a high calorific value gas (synthesis gas or syngas), a biofuel (bio oil or pyrolysis oil) and a solid residue (char). Depending on the final temperature, MSW pyrolysis will yield mainly solid residues at low temperatures, less than 4500C, when the heating rate is quite slow, and mainly gases at high temperatures, greater than 8000C, with rapid heating rates. At an intermediate temperature and under relatively high heating rates, the main product is a liquid fuel popularly known as bio oil.

Wide Range of Products

Bio oil is a dark brown liquid and can be upgraded to either engine fuel or through gasification processes to a syngas and then biodiesel. Pyrolysis oil may also be used as liquid fuel for diesel engines and gas turbines to generate electricity Bio oil is particularly attractive for co-firing because it can be relatively easy to handle and burn than solid fuel and is cheaper to transport and store. In addition, bio oil is also a vital source for a wide range of organic compounds and specialty chemicals.

Syngas is a mixture of energy-rich gases (combustible constituents include carbon monoxide, hydrogen, methane and a broad range of other VOCs). The net calorific value (NCV) of syngas is between 10 and 20MJ/Nm3. Syngas is cleaned to remove particulates, hydrocarbons, and soluble matter, and then combusted to generate electricity. Diesel engines, gas turbines, steam turbines and boilers can be used directly to generate electricity and heat in CHP systems using syngas and pyrolysis oil. Syngas may also be used as a basic chemical in petrochemical and refining industries.

The solid residue from MSW pyrolysis, called char, is a combination of non-combustible materials and carbon. Char is almost pure carbon and can be used in the manufacture of activated carbon filtration media (for water treatment applications) or as an agricultural soil amendment.

Thermal Conversion of Biomass

A wide range of technologies exists to convert the energy stored in biomass to more useful forms of energy. These technologies can be classified according to the principal energy carrier produced in the conversion process. Carriers are in the form of heat, gas, liquid and/or solid products, depending on the extent to which oxygen is admitted to the conversion process (usually as air). The major methods for thermal conversion of biomass are combustion in excess air, gasification in reduced air, and pyrolysis in the absence of air.

biomass-gasification

Combustion

Conventional combustion technologies raise steam through the combustion of biomass. This steam may then be expanded through a conventional turbo-alternator to produce electricity. A number of combustion technology variants have been developed. Underfeed stokers are suitable for small scale boilers up to 6 MWth. Grate type boilers are widely deployed. They have relatively low investment costs, low operating costs and good operation at partial loads. However, they can have higher NOx emissions and decreased efficiencies due to the requirement of excess air, and they have lower efficiencies.

Fluidized bed combustors (FBC), which use a bed of hot inert material such as sand, are a more recent development. Bubbling FBCs are generally used at 10-30 MWth capacity, while Circulating FBCs are more applicable at larger scales. Advantages of FBCs are that they can tolerate a wider range of poor quality fuel, while emitting lower NOx levels.

Co-Firing

Co-firing or co-combustion of biomass 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 involves utilizing existing power generating plants that are fired with fossil fuel (generally coal), and displacing a small proportion of the fossil fuel with renewable biomass fuels.

Co-firing has the major advantage of avoiding the construction of new, dedicated, waste-to-energy power plant. Co-firing may be implemented using different types and percentages of wastes in a range of combustion and gasification technologies. Most forms of biomass wastes are suitable for co-firing. These include dedicated municipal solid wastes, wood waste and agricultural residues such as straw and husk.

Gasification

Gasification of biomass 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.

If gasifiers are ‘air blown’, atmospheric nitrogen dilutes the fuel gas to a level of 10-14 percent that of the calorific value of natural gas. Oxygen and steam blown gasifiers produce a gas with a somewhat higher calorific value. Pressurized gasifiers are under development to reduce the physical size of major equipment items.

A variety of gasification reactors have been developed over several decades. These include the smaller scale fixed bed updraft, downdraft and cross flow gasifiers, as well as fluidized bed gasifiers for larger applications. At the small scale, downdraft gasifiers are noted for their relatively low tar production, but are not suitable for fuels with low ash melting point (such as straw). They also require fuel moisture levels to be controlled within narrow levels.

Pyrolysis

Pyrolysis is the term given to the thermal degradation of wood in the absence of oxygen. It enables biomass 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. These products are generated in roughly equal proportions with slow pyrolysis. Using fast pyrolysis, bio-oil yield can be as high as 80 percent of the product on a dry fuel basis.

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.

Biomass Gasification Process

Biomass gasification involves burning of biomass in a limited supply of air to give a combustible gas consisting of carbon monoxide, carbon dioxide, hydrogen, methane, water, nitrogen, along with contaminants like small char particles, ash and tars. The gas is cleaned to make it suitable for use in boilers, engines and turbines to produce heat and power (CHP).

Biomass gasification provides a means of deriving more diverse forms of energy from the thermochemical conversion of biomass than conventional combustion. The basic gasification process involves devolatization, combustion and reduction.

During devolatization, methane and other hydrocarbons are produced from the biomass by the action of heat which leaves a reactive char.

During combustion, the volatiles and char are partially burned in air or oxygen to generate heat and carbon dioxide. In the reduction phase, carbon dioxide absorbs heat and reacts with the remaining char to produce carbon monoxide (producer gas). The presence of water vapour in a gasifier results in the production of hydrogen as a secondary fuel component.

There are two main types of gasifier that can be used to carry out this conversion, fixed bed gasifiers and fluidized bed gasifiers. The conversion of biomass into a combustible gas involves a two-stage process. The first, which is called pyrolysis, takes place below 600°C, when volatile components contained within the biomass are released. These may include organic compounds, hydrogen, carbon monoxide, tars and water vapour.

Pyrolysis leaves a solid residue called char. In the second stage of the gasification process, this char is reacted with steam or burnt in a restricted quantity of air or oxygen to produce further combustible gas. Depending on the precise design of gasifier chosen, the product gas may have a heating value of 6 – 19 MJ/Nm3.

Layout of a Typical Biomass Gasification Plant

The products of gasification are a mixture of carbon monoxide, carbon dioxide, methane, hydrogen and various hydrocarbons, which can then be used directly in gas turbines, and boilers, or used as precursors for synthesising a wide range of other chemicals.

In addition there are a number of methods that can be used to produce higher quality product gases, including indirect heating, oxygen blowing, and pressurisation. After appropriate treatment, the resulting gases can be burned directly for cooking or heat supply, or used in secondary conversion devices, such as internal combustion engines or gas turbines, for producing electricity or shaft power (where it also has the potential for CHP applications).

 

See some of our favorite inspirational quotes