Tag Archives: Application of Biochar

Why Fossil Fuels are Preferred Over Biomass by Industries?

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Biomass can play a key role in economic development and emerge as a significant alternative to fossil fuels. In this article, we will discuss why fossil fuels are preferred over biomass fuel by the industrial sector.

biomass collection

 

Pyrolysis and the Promise of Biochar

The end application of biomass mostly depends on the feedstock type and the char conversion process. When processed under controlled conditions, biomass converts to char (or biochar). With the presence of high carbon content in biochar, they are highly dependent on the processing conditions of biomass (or fuel), e.g. wood char produced from pyrolysis at low or no air flow can expect to have high carbon and hydrogen with minimal minerals/inorganic presence.

Gas produced under same condition will have a high presence of heavy aromatic carbon and nitrogen gas. However, under the same conditions, if physical structure of biomass varies, the output results can fluctuate to a significant level.

The temperature, pressure, elemental composition, particle size, physical structure (e.g. density, moisture presence, molecular structure, pore size), heating rate, the maximum temperature of process, retention time during the conversion process can change the composition of biochar produced.

Biomass when converted to char has multiple applications with minimal effect on the environment. It has applications in toxic metal remediation and can remove harmful contaminants from soil which can damage plant growth and soil nutrients.

uses of char

Char has potential to stabilise cadmium, lead, chromium, zinc, but they are found to be most effective in stabilisation of lead and copper.  Researchers have found the potential application of biochar in a range of applications, viz. carbon sequestration, solid waste management, green electricity production, wastewater treatment, iron making process and building construction.

Why Fossil Fuel is Preferred Over Biomass Fuel?

Despite the significant contrast of applications and proven to have minimal effect on the environment, why is biomass not preferred or unsuccessful to attract the commercial sector? The answer relies on biomass processing technologies that still need to develop economically feasible. Besides fuel cost, the initial setup of biomass-based technologies need high capital cost, operation and maintenance cost, which eventually lead to a significantly higher cost of end application when compared with fossil fuels.

In most FMCG, sugarcane and fruit-based industries, biomass is produced as their waste, and legal compliances expect them to dispose of their waste sustainably. Industries spend substantial money to dispose of their waste in agreement with legal and environmental regulations. Researchers termed it a negative cost, which means that industries intend to pay to take this biomass off from their facility.

bagasse cogeneration

This could bring a possible opportunity to biomass processing plants to get paid or acquire fuel at no or negative cost. But most processing facilities are far from fuel (or biomass waste) sources, and cost of transportation are significant enough to compare the economics of fuel acquirement with fossil fuel costs. Moreover, processing technologies need cleaning and maintenance which further add up to the cost.

The overall economics of biomass-based electricity and any other end-use process cost higher than fossil fuels, making it very difficult to attract industries to invest in biomass over fossil fuels. Research suggests that biomass processing facilities that are available within the periphery of 200km from the fuel source will cost biomass (or fuel) at zero to negative value, improving the overall economics to a significantly comparable level to fossil fuels.

The Way Forward

To address this issue, small-scale plants must be installed in nearby areas and critical focus is vital on economically small scale biomass processing plants. Considerable research work is going on with small scale gasification plants capable of producing electricity at a small scale, but that is still under pilot project and no large-scale implementation has been found so far. Pyrolysis plants are also under the research zone, producing biochar, but this method is still under research development.

To reach targets of global temperature and carbon emissions into the atmosphere set by the UN at Climate Summit 2015, this area of research is a potentially critical area that can play a significant role in overtaking biomass over fossil fuels.

Overview of Biomass Pyrolysis Process

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Biomass pyrolysis is the thermal decomposition of biomass occurring in the absence of oxygen. It is the fundamental chemical reaction that is the precursor of both the combustion and gasification processes and occurs naturally in the first two seconds. The products of biomass pyrolysis include biochar, bio-oil and gases including methane, hydrogen, carbon monoxide, and carbon dioxide.

The biomass pyrolysis process consists of both simultaneous and successive reactions when organic material is heated in a non-reactive atmosphere. Thermal decomposition of organic components in biomass starts at 350 °C–550 °C and goes up to 700 °C–800 °C in the absence of air/oxygen. The long chains of carbon, hydrogen and oxygen compounds in biomass break down into smaller molecules in the form of gases, condensable vapours (tars and oils) and solid charcoal under pyrolysis conditions. Rate and extent of decomposition of each of these components depends on the process parameters of the reactor temperature, biomass heating rate, pressure, reactor configuration, feedstock etc

Depending on the thermal environment and the final temperature, pyrolysis will yield mainly biochar at low temperatures, less than 450 0C, when the heating rate is quite slow, and mainly gases at high temperatures, greater than 800 0C, with rapid heating rates. At an intermediate temperature and under relatively high heating rates, the main product is bio-oil.

Slow and Fast Pyrolysis

Pyrolysis processes can be categorized as slow or fast. Slow pyrolysis takes several hours to complete and results in biochar as the main product. On the other hand, fast pyrolysis yields 60% bio-oil and takes seconds for complete pyrolysis. In addition, it gives 20% biochar and 20% syngas.  Fast pyrolysis is currently the most widely used pyrolysis system.

The essential features of a fast pyrolysis process are:

  • Very high heating and heat transfer rates, which require a finely ground feed.
  • Carefully controlled reaction temperature of around 500oC in the vapour phase
  •  Residence time of pyrolysis vapours in the reactor less than 1 sec
  • Quenching (rapid cooling) of the pyrolysis vapours to give the bio-oil product.

Advantages of Biomass Pyrolysis

Pyrolysis can be performed at relatively small scale and at remote locations which enhance energy density of the biomass resource and reduce transport and handling costs.  Heat transfer is a critical area in pyrolysis as the pyrolysis process is endothermic and sufficient heat transfer surface has to be provided to meet process heat needs. Biomass pyrolysis offers a flexible and attractive way of converting organic matter into energy products which can be successfully used for the production of heat, power and chemicals.

A wide range of biomass feedstock can be used in pyrolysis processes. The pyrolysis process is very dependent on the moisture content of the feedstock, which should be around 10%. At higher moisture contents, high levels of water are produced and at lower levels there is a risk that the process only produces dust instead of oil. High-moisture waste streams, such as sludge and meat processing wastes, require drying before subjecting to pyrolysis.

Furthermore, the bio-char produced can be used on the farm as an excellent soil amender as it is highly absorbent and therefore increases the soil’s ability to retain water, nutrients and agricultural chemicals, preventing water contamination and soil erosion. Soil application of bio-char may enhance both soil quality and be an effective means of sequestering large amounts of carbon, thereby helping to mitigate global climate change through carbon sequestration.  Use of bio-char as a soil amendment will offset many of the problems associated with removing crop residues from the land.

Biomass pyrolysis has been garnering much attention due to its high efficiency and good environmental performance characteristics. It also provides an opportunity for the processing of agricultural residues, wood wastes and municipal solid waste into clean energy. In addition, biochar sequestration could make a big difference in the fossil fuel emissions worldwide and act as a major player in the global carbon market with its robust, clean and simple production technology.