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3.0 Proposed Technology

Slow Pyrolysis Process 

 

Pyrolysis is the heating of an organic material, such as biomass, in the absence of oxygen.  Because no oxygen is present the material does not combust but the chemical compounds (i.e. cellulose, hemicellulose and lignin) that make up that material thermally decompose into combustible gases and charcoal.  Most of these combustible gases can be condensed into a combustible liquid, called pyrolysis oil (bio-oil), though there are some permanent gases (CO2, CO, H2, light hydrocarbons). 

 

Thus pyrolysis of biomass produces three products:

  • one liquid (bio-oil)

  • one solid (bio-char)

  • one gaseous (syngas)

 

The proportion of these products depends on several factors including the composition of the feedstock and process parameters.  However, all things being equal, the yield of bio-oil is optimized when the pyrolysis temperature is around 500 °C and the heating rate is high (i.e. 1000 °C/s) i.e. fast pyrolysis conditions. Under these conditions bio-oil yields of 60-70 wt% of can be achieved from a typical biomass feedstock, with 15-25 wt% yields of bio-char.  The remaining 10-15 wt% is syngas.  Processes that use slower heating rates are called slow pyrolysis and bio-char is usually the major product of such processes.

 

THE PROCESS

 

The 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 bio-char at low temperatures, less than 450 °C, when the heating rate is quite slow, and mainly gases at high temperatures, greater than 800 °C, with rapid heating rates. At an intermediate temperature and under relatively high heating rates, the main product is bio-oil.

YIELDS

 

Bio-oil

Bio-oil is a dark brown liquid and has a similar composition to biomass. It has a much higher density than woody materials which reduces storage and transport costs. Bio-oil is not suitable for direct use in standard internal combustion engines. Alternatively, the oil can be upgraded to either a special engine fuel or through gasification processes to a syngas and then bio-diesel. Bio-oil is particularly attractive for co-firing because it can be more readily handled and burned than solid fuel and is cheaper to transport and store.

 

Bio-oil can offer major advantages over solid biomass and gasification due to the ease of handling, storage and combustion in an existing power station when special start-up procedures are not necessary. In addition, bio-oil is also a vital source for a wide range of organic compounds and speciality chemicals..

 

Bio-char

Bio- char is used on the farm as an excellent soil amender that can sequester carbon.  Bio-char 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.

 

Syngas

Syngas can be used directly as an energy source (e.g. gas turbines) or as an intermediate in the production of synthetic natural gas, ammonia and other energy sources.  Syngas can also be used as an intermediary in producing synthetic petroleum or liquid fuel (e.g. diesel fuel).  In addition, syngas has the potential to produce many of the products and chemicals currently created from petroleum. 

ADVANTAGES AND DISADVANTAGES

 

Advantages of pyrolysis:

 

  • It can be used for all types of solid products and can be more easily adapted to changes in feedstock composition than alternative approaches

  • The technology is relatively simple and can be made compact and lightweight and thus is amenable to spacecraft operations

  • It can be conducted as a batch, low pressure process, with minimal requirements for feedstock pre-processing

  • The technology can be designed to produce minimal amounts of unusable by-products

  • It can produce potentially valuable chemicals and chemical feedstock

 

Disadvantages of pyrolysis:

 

  • Technology is still evolving           

  • Markets are yet to be developed for char product and pyrolysis liquids

  • Pyrolysis plants require a certain amount of materials to work effectively

.

SUSTAINABILITY OF TECHNOLOGY

 

The pyrolysis process can be self-sustained, as combustion of the syngas and a portion of bio-oil or bio-char can provide all the necessary energy to drive the reaction. Pyrolysis is considered to be one of the sustainable solutions that may be economically profitable in large scales and minimise environmental concerns especially in terms of:

 

  • Waste minimization

    • It provides an opportunity for the processing of agricultural residues, wood wastes and municipal solid waste into clean energy.

 

  • Carbon sequestration

    • The product of bio-char is being considered for carbon sequestration, with the aim of mitigation of global warming. The solid, carbon-containing char produced can be sequestered in the ground, where it will remain for several hundred to a few thousand years.

 

  • Soil amendment Energy/Heat supply

    • Bio-char improves the soil texture and ecology, increasing its ability to retain fertilizers and release them slowly. It naturally contains many of the micronutrients needed by plants, such as selenium. It is also safer than other "natural" fertilizers such as animal manure, since it has been disinfected at high temperature. And, since it releases its nutrients at a slow rate, it greatly reduces the risk of water table contamination.

 

  • Development of rural areas

    • The livelihood of most people in rural of Perak is hinged on agriculture. They do cultivation of mainly maize and a few grain crops on a communal scale. They also do cattle rearing and goat rearing on animal husbandry. Thus, the products of slow pyrolysis especially bio-char can help increase the yield and productivity of their crops.

 

 

REASON OF CHOOSING THIS TECHNOLOGY

 

Comparison of pyrolysis with other technologies

 

This is the comparison between pyrolysis with other technology. The comparison will be divided into three parts; Definition and processes, advantages and disadvantages and also recommendation of the process. The technology that are being compared are Pyrolysis, Plasma Gasification (PG), Bioremediation and Thermophilic Digestion (TD).
 

Through definition, Pyrolysis is the heating of organic material with the absence of oxygen. For PG, it is the ionization of gas and catalyzed the organic material into synthetic gas and solid waste. Bioremediation is the process of degrading environmental containment into less toxic form via microorganism. Lastly for TD, is a thermal decomposition process which combine with the present microorganism to increase the decomposition processes. Comparing all this four processes, pyrolysis produces bio-gas, bio-oil, and bio-char, PG produces synthetic gas and solid waste and TD produces CO2, H2 and CH4 while Bioremediation reduces the toxicity level only.
 

Next is the advantages and disadvantages of each process. Below are the comparison of advantages and disadvantages for each processes. 

 


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Finally is the comparison of sustainability for all four processes. Pyrolysis and Plasma Gasification (PG) are both new emerging technology which are constantly evolving. Bioremediation have a full potential which can be used to cure wide range of toxic compound which can pave the road to future. Thermal Digestion (TD) solves the problem to waste management issue which combine both combustion and bacteria usage. All the technology listed are good for the future better betterment. However, we found that pyrolysis is the most suitable technology to be apply to manage the wastes for our case study. As we know, the waste disposed from the supermarket is consists of different types of raw food like vegetable, meat, fruits and so on. The ratio or compositions of these wastes will always different from day to day depending on the customers demand. To solve this problem, we choose pyrolysis because pyrolysis can be used for all type of solid products and can be easily adapted to the change in feedstock composition compare to the alternative technology. Another reasons that we choose this technology is that it can be designed to produce minimal amounts of unusable by-products. Also, because Perak is vast in agricultural activities, choosing slow pyrolysis is a method to potentially induce the production of agricultural field as pyrolysis favours bio-char that acts like fertilizers for plants.

 

Catalyst Involvement

 

Catalysts for pyrolysis can be differentiated based on the step reaction taken.

 

Zeolites

Zeolites is commonly implemented in fast pyrolysis due to cheap in cost and the favourable catalysis on producing more aromatics and olefins in the bio-oil produced from the fast pyrolysis process.. In specialized catalytic fast pyrolysis, zeolites can be added immediately into the reactor to initialize series of dehydration, decarbonylation and oligomerization reactions to produce high yield of aromatics and olefins. Since bio-oil is acidic and insoluble with petroleum-based fuels with high oxygen component, zeolites improve the bio-oil product to reach desired condition for proper usage.

 

Types of zeolites include H-forms zeolites (Beta, Y, ZSM-5) are commonly studied in fast pyrolysis. Prins and Bridgwater (2010) concluded their study on zeolite catalysis with HZSM-5 being most suitable catalyst for highest production of hydrocarbons with 55 wt % of hydrocarbon determined theoretically.

 

There are two ways the zeolites can be added in the catalytic fast pyrolysis. First, addition of zeolites can be added into in-bed and ex-bed catalysis when the product formed is passed to combustor and condenser respectively. Second , addition separation process known as zeolite cracking method could be implemented onto the product streams. Similarity between the two process mentioned is the byproduct as both step process produce coke , bio-oil and other component including carbon monoxide , carbon dioxide and water.

 

HDO (Hydro deoxygenation)

The reaction is done with multiple steps reaction: stabilization under hydrogen pressure at 250 -275 ℃ , water separation , hydro treatment at 300-450℃ . HDO reaction requirement for catalyst of Molybdenum based catalyst, including sulphided CoMo and NiMo. Other types of catalyst would be Ruthenium-based Ru/C. Despite overall process contribute to the complete deoxygenation, yet the reaction priority is not focused on total oxygen removal. Further concern for the production is distillable bio-oil and avoidance of repolymerisation process as such process will create less desired products.

 

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