Biomass Gasification
The gasification is a thermochemical process in which a carbonaceous substrate (carbon, biomass, plastic) is transformed in a fuel gas through a series of reactions that occur in presence of an gasification agent (air, oxygen, water vapor and hydrogen). The generated gas can be utilized to generate electricity or thermal energy.
The gasification process is divided in four steps: Drying, Pyrolisis, Reduction and Combustion.
http://www.tecnoredconsultores.com.ar/gasi.html, modified.
The first reaction is the drying process. in temperature between 100°C and 200°C the biomass is heated and the moisture becomes water vapor.
The second reaktion is the process of thermical decomposition, the pyrolisis. The principal components of wood and biomass are cellulose, hemicellulose and lignin. With temperatures of 150°C to 500°C these molecular connections break up and produce hydrocarbonates.
As the process reaches temperatures above 500°C, the oxidation/combustion happens due to the solid products, liquids and obtained gases from pyrolising reacting with oxygen and further increase the temperature.
C + O2 --> CO2
C + 0,5 O2 <--> CO
The last step is reduction where the inflamable components of the syngas are produced in line with the following reactions and temperatures between 800°C and 1100°C.
C + CO2 <--> 2CO
C + H2O <--> CO + H2
CO + H2O <--> CO2 + H2
C + 2H2 <--> CH4
Utilization
The produced gas from the gasification is commonly used by biomass plants in the process of combustion to produce heat and electricity. By cogeneration the transformation can reach a high efficiency.
In solid oxide fuel cells it's possible to transform the gas into electricity directly.
In the Dominican Republic there is the potential to adapt gasifier in sugarcane mills.
In addition the gas can be used as a syngas for chemical synthesis of various products because of its compounds of carbon-monoxide and hydrogen. This procedure deals mainly with hydrogen and ammonia production and the following Haber-Bosch-Synthesis. Also the synthesis of methanol and the Fischer-Tropsch-Synthesis to produce biofuel/BtL (Biomass to Liquid).
At last there's the use of gasification on a smaller scale: microgasification. Still 2.7 billion people in the world cook with solid fuels. Traditional stoves produce carbon monoxide emissions of 29g/MJ which cause respiratory health problems in humans. The example of microgasification wants to substitute firewood stoves and give the posibility of cleaner and healthier stoves. In comparison, improved microgasifier have an emission of 6g/MJ and that means it's as clean as cooking with gas (WHO, 2013). Additionally to the reduction of air contamination it also improves the process' thermal efficiency and it is easier to light than carbon.
Potential in the dominican republic
Currently the Dominican Republic imports more energy than it produces. According to a report in energetical balance, in 2015 44.078,15 kbbl of fuel were imported to the country. Also energy consumption is mainly covered by fossil fuels. Gasification offers the possibility of energy independency and sustainability. The agricultural sector produces waste products which have the potential to be used as a source for bioenergy. In the Dominican Republic typical examples hereof are rice husks, coffee pulp and wastes in the production of cacao, banana and sugarcane.
Gasification in the laboratory for renewable energies
The equipment in gasification is a fixed-bed reactor with a nominal electric potential of 20kWh.
Areas in development and consultancy:
- Pretreatment of biomass: Drying
- Splinting/Chopping · Drying · Grinding · Pelleting
- Determination of the gases
- Technology of gasification for electricity production
- Development of process and gas cleaning
Analysing process of the gas determining the concentration in %H2, %CO, %CH4, %CnHm, %CO2 and %O2.
