Bioenergy

Biomass

The traditional use of biomass for cooking involves burning wood or charcoal in simple cookstoves. In many countries (such as Haiti), and in the villages of many others (such as India) this is still the principal form of cooking for the majority of the population. However, cooking with wood and charcoal (or worse with dung and agricultural residues) brings severe health impacts due to the smoke produced by the stoves, and the fact that cooking often takes place in the home where children are present or nearby.

Cooking with wood or charcoal produces dangerous levels of air pollution which is harmful for women and children

In many countries where biomass is used for cooking, there are national programs intended to promote the introduction of cleaner fuels for cooking—either bottled LPG gas or electricity. In spite of these programs, the global consumption of traditional biomass fuels has been increasing slowly—as population increases have outpaced the introduction of more modern fuels for cooking.

Modern bioenergy includes wood pellets used as fuel in power plants,  liquid fuels used in the transport sector, and fuel gases containing methane produced from organic waste. 

Pellet power

The Drax power plant in Yorkshire, UK, is the world’s largest biomass-pellet-based electricity generator. Three coal-fired units with a combined capacity of 1.9 GW have been converted to using biomass pellets as fuel[3].   

The Drax power station consists of six 660 MW generating units producing at full output just under 4000 MW. Drax began burning biomass in 2003, in conjunction with coal in a co-firing arrangement used in all six generating units. In 2012, the company confirmed its plans to operate three of the six units entirely on biomass pellets, and the first converted unit began generating electicity in 2013.

The Drax power plant in the UK burns both coal and wood pellets. The four storage domes in the foreground hold the wood pellets.

With three generating units now converted to wood pellet fuel, the power plant burns about 7 to 8 million tonnes of wood pellets a year [11].

Most of the wood pellets for Drax are imported from North America. The USA is the world’s main producer and exporter of wood pellets. In 2017, the US had the capacity to produce over 10 Mt of pellets annually. Actual production was 5.3 Mt of which 4.7 Mt was exported to Europe.  Other major producers and exports of wood pellets are Canada and Latvia [5].

Three UK ports handle the transatlantic shipments of pellets destined for Drax: Tyne, Hull and Immingham. Biomass is a third lighter than coal and vulnerable to rain, which means that transport from the ports by rail is done in specially designed covered wagons that are much larger than coal wagons. Each wagon holds just over 70 tonnes of pellets. Arriving at the Drax plant, the pellets are automatically transferred to four storage units each capable of holding 110,000 m3 of biomass [12].

The company claims that converting from wood to coal will reduce emissions of carbon dioxide by more than 80 % relative to coal, but this claim is strongly disputed by several reputable scientific studies.

Clean? Not quite

One important aspect to consider at the outset is that all biofuels contain carbon.  When burned to produce heat or used as fuel in an engine, they produce emissions of carbon dioxide just like fossil fuels.  In fact, wood pellet-burning power plant emit more carbon dioxide per unit of electricity generated than coal. Their advantage, compared to fossil fuels, lies in the fact that the carbon produced during combustion is carbon that was absorbed by the wood when it was growing. Many people therefore consider biofuels to be ‘carbon neutral’—meaning that when used as fuel, they do not produce additional amounts of carbon. They simply return to the atmosphere what they had previously removed.

However, this view is simplistic. Several detailed and careful studies have shown that when the full life-cycle of the biomass fuel is taken into account, including land use changes and the emissions produced by harvesting and transporting the fuel to a power plant, biomass fuels actually result in the generation of additional amounts of carbon dioxide and other greenhouse gases. The use of wood as a fuel in any large scale application is not carbon neutral.

A very detailed analysis of using forest biomass for power generation was conducted in Massachusetts in 2010. Noting that forest biomass generally emits more greenhouse gases than fossil fuels per unit of energy produced, the study confirmed that over time, the re-growth of the harvested forest eventually removes this excess carbon from the atmosphere. Dubbing this excess the ‘carbon debt’, the analysis showed that after several years, biomass begins to yield carbon dividends in the form of greenhouse gas emissions that are lower than would have occurred if fossil fuels had been used to produce the same amount of energy.  But getting to this point takes time–often several decades.

Enviva Ahoskie wood pellet mill in North Carolina [11]

If forest biomass is used as a fuel to replace oil for combined heat and power (CHP), it takes about five years before there is a net benefit in terms of reduced emissions. But if forest biomass replaces a coal-fired plant, it can take as long as 21 years before there is a net benefit.  Looking ahead 40 years to 2050, the report calculates that the replacement of oil-fired thermal/CHP capacity with biomass thermal/CHP would fully offset the carbon debt and lower greenhouse gas levels compared to what would have been the case if fossil fuels had been used over the same period—approximately 25% lower.  For biomass replacement of coal-fired plants, the net cumulative emissions in 2050 are approximately the same, but replacing a gas-fuelled plant with forest biomass would not yield any benefit at all—emissions would be substantially higher with a biomass fuelled plant. [1]

The concept of carbon neutrality was again called into question in 2018 when the European Academies Science Advisory Council (EASAC) issued a press release strongly cautioning that bioenergy from forests is not always carbon neutral and may in fact increase carbon emissions. The EASAC scientists noted that carbon neutrality involves a ‘payback’ period (the time taken for forests to reabsorb the CO2 emitted during biomass combustion), which ranges from decades to hundreds of years—depending on the type of biomass and what happens to the forest and land area after harvesting. [2]

This conclusion was confirmed by a 2018 study that found that although bioenergy from wood can lower long-run CO2 concentrations compared to fossil fuels, its first impact is an increase in CO2 which in fact worsens global warming over the critical period through to 2100–even if if the wood replaces coal, the most carbon-intensive fossil fuel. The authors go on to state:

Declaring that biofuels are carbon neutral as the EU and others have done , erroneously assumes forest regrowth quickly and fully offsets the emissions from biofuel production and combustion. The neutrality assumption is invalid because it ignores the transient, but decades to centuries long, increase in CO2 caused by biofuels. [12].

Notwithstanding the fact that wood pellet fuel is not carbon neutral, the global production and trade of pellets used for power production and heating has continued to expand: with production reaching close to 30 million tonnes in 2017. About half this amount was used for residential and commercial heating—most notably in Europe, and about half used for power generation.

Europe is the major market for electricity generation—especially the United Kingdom which burned 7.5 Mt of wood pellets for power generation in 2017.

In 2018, substantial amounts of wood pellets were being exported from the southeast US to Europe. In North Carolina, the wood fuel industry was logging about 200 km2 of forest a year to meet the demand in Europe.[4] 

Biofuels

The production and consumption of liquid biofuels is mainly concentrated in the USA, Brazil, and Europe.  The US and Brazil are by far the largest producers of biofuels, followed by Germany, Argentina, China and Indonesia.

The main biofuels are ethanol, biodiesel (fatty acid methyl ester or FAME fuels), and fuels produced by treating animal and vegetable oils and fats with hydrogen (called hydrotreated vegetable oil, HVO, and hydrotreated esters and fatty acids called HEFA).

About two thirds of biofuels is ethanol; 29% was FAME biodiesel; and 6% was HVO/HEFA fuels.  The use of biomethane as a transport fuel, while growing rapidly, contributed less than 1% of the biofuel total.[7]

The US and Brazil are the main ethanol producers—most of which is used in their countries. In the US, 90% of the ethanol is produced from maize and blended with gasoline in a 10% mixture called E10 gasoline. In Brazil, ethanol is produced from sugar cane. China, Canada and Thailand also produce ethanol.

Since biofuels also produce emissions of carbon when combusted in an engine, there is a continuing debate about the degree to which biofuels are actually carbon neutral. And when ethanol is produced from maize—as it is in the US and Canada, a further controversy centers on the ‘food versus fuel’ dilemma.

Advanced biofuels

The term advanced biofuel or second-generation biofuel refers to fuels that are not derived from biomass sources that could be used as food or animal feed—such as maize.  The main types of advanced biofuels are:

  • Ethanol derived from cellulose, hemicellulose, or lignin.
  • Ethanol derived from waste material, including crop residue, other vegetative waste material, animal waste, and food waste and yard waste.
  • Biomass-based diesel.
  • Butanol or other alcohols produced through the conversion of organic matter from renewable biomass.
  • Other fuel derived from cellulosic biomass.

The aim is to produce fuels that demonstrate improved life-cycle carbon savings compared to biofuels produced from sugar, starch, and oils, as well as fuels with less impact on land use—for example fuels from waste and residues. Some advanced biofuels (known as ‘drop in biofuels’) can replace fossil fuels directly in transport systems including aviation, or for blending in high proportions with conventional fuels.

The problem with advanced biofuels produced using chemical processes is that the production requires considerable amounts of energy that itself produces greenhouse gases. There are also exhaust gases when the biofuel is combusted in an engine. To this must be added the emissions produced in collecting, transporting and processing the feedstock materials.

If carbon capture and storage technology can be integrated into biofuel production, life-cycle emissions of carbon would be substantially reduced.  But as of 2018, only a limited number of large-scale projects have demonstrated the technical viability of this technology.  

Where electric forms of transport are feasible, this is by far the best option—always assuming that the electricity is generated from renewable sources of energy.  But for aviation and international marine transport, biofuels may be the only viable, low-carbon option at the present time.

In this regard, several airlines have experimented with the use of biofuels for long-haul flights. Virgin Australia and Qantas have powered planes with biofuels—the latter signing a long-term supply contract with Agrisoma (France) to supply fuels based on carinata oil seed.  Hainan Airlines has made a trans- Pacific flight from Beijing to Chicago using biofuel derived from waste cooking oil.

For maritime transport, the use of biofuels to power ships has also been demonstrated. For instance, following initiatives by the US Navy, the Australian Navy has reportedly been trialling biofuels in its fleet.  On the railroads, trials are also underway. In the Netherlands, Arriva is supplying 16 new trains fuelled with biodiesel, and Indian Railways is experimenting with the use of biodiesel, compressed biogas and ethanol to power its trains.[8]

This section has only skimmed the surface of biofuel technology. However, it should be recognized that while biofuels do not in principle inject additional fossil fuel carbon into the global carbon cycle, their production and transportation require energy inputs from conventional fossil fuels. The life cycle emissions of biofuels may be less than fossil fuels, but they are far from being zero. 

Biogas

Biogas is a mixture of methane and carbon dioxide produced by the anaerobic digestion of organic materials—including food waste, sewage, manure, animal dung, and plants gown specifically for the purpose. Small biogas systems have been used in Asia for decades and were pioneered in China where tens of millions of small household systems have been constructed over the last 50 years, running on animal waste and even human night soil. There are also several million household biogas plants operating in India.  Small biogas plants generate a gas that can be used for cooking—thus avoiding cutting down trees for fuel and the noxious air pollution caused by burning wood, charcoal and dung in the home. 

Globally, as many as 50 million biogas cookstoves are estimated to have been installed at the end of 2016, with about 126 million people using biogas for cooking mainly in China and India.  The use of biogas for cooking is growing elsewhere in Asia—in Bangladesh, Cambodia, Indonesia and Nepal; and also in sub Saharan Africa—Ethiopia, Kenya, and Tanzania.  The Africa Biogas Partnership Programme has promoted more than 58,000 biogas plants–installed in Burkina Faso, Ethiopia, Kenya, Tanzania and Uganda since 2009. [9]

However, there is increasing interest in larger-scale systems—particularly in biogas produced from feedlots, landfills, and food processing operations where substantial amounts of biogas can be produced.  Biogas can be upgraded to biomethane by removing the carbon dioxide and other gases, enabling the gas to be more easily used for transport or for injection directly into natural gas pipelines.  Applications vary: in the US and Sweden, biomethane is used mainly for transport, while in the United Kingdom it is used mainly as a pipeline gas.

More than 500 biomethane production facilities now exist in Europe.  For food processing factories that produce biodegradable waste that must be disposed of correctly, it makes economic sense to produce biogas from the waste and to use the fuel in the factory to produce heat or steam for the processing of the food.  For instance, the Swedish beer manufacturer Carlsberg converted its brewery in Falkenberg, Sweden to 100 % biogas in 2017. Not all this biogas is produced in the brewery—most of it is piped in from local energy supplier Orsted AB.[10]


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For more information check out these sources:

[1] The Biomass sustainability and carbon policy study by the Manomet Center for Conservation Sciences is available here: //www.manomet.org/wp-content/uploads/old-files/Manomet_Biomass_Report_Full_June2010.pdf
[2] See the press release issued by the European academies science advisory council, and the commentary on forest bioenergy and carbon neutrality issued on the same day.  Available at: //easac.eu/fileadmin/PDF_s/reports_statements/Carbon_Neutrality/EASAC_Press_Release_on_Carbon_Neutrality_15_June_2018.pdf
[3] See: Renewables 2018 Global Status Report.
[4] See: Burning wood as renewable energy threatens Europe’s climate goals.  At: //insideclimatenews.org/news/21062018/forest-biomass-renewable-energy-paris-climate-change-emissions-logging-wood-pellets-electricity/
[5] ibid
[7] ibid
[8] ibid
[9] Ibid
[10] See: Carlsberg launches carbon neutral brewery in Sweden, at //www.beveragedaily.com/Article/2017/11/27/Carlsberg-launches-carbon-neutral-brewery-in-Sweden
[11] See: Dirty deception: How the wood biomass industry skirts the Clean Air Act. Environmenntal Integrity Project, April 2018.
[12] Sterman J.D. et.al: Does replacing coal with wood lower CO2 emissions? Dynamic lifecycle analysis of wood bioenergy. Environmental Research Letters.13(2018)