Three main routes exist to thermo chemically convert biomass into energy: combustion, gasification and pyrolysis/htl.
Combustion for the generation of heat and/or electricity (via steam) is widely used, but its efficiencies are rather low, and rated at 15% for small plants to 30% for larger and newer plants (Bridgewater, 2003), although combined heat and power (CHP)plants can have efficiencies up to 85%. Only the combustion of waste or residues is today economically feasible, although stack emissions and ash handling remain technical problems. Large-scale gasification of biomass has been successfully demonstrated, but it is still relatively expensive in comparison to energy from fossil fuel. Various demonstration units were recently stopped, although gasification is capable of producing power from biomass at competitive price levels on a somewhat longer term. Biomass gasification will only be able to penetrate the market if it is integrated into a bio-energy system.
Pyrolysis is the thermal decomposition in the complete absence of an oxidizing agent (air or oxygen), or with such a limited supply that combustion or gasification do not occur to any appreciable extent. Pyrolytic cracking of biomass yields mainly liquids, together with a solid residue (char) and gas. Dried seaweed, which is low on water, can easily convert into bio-crude, gas and char and the method preferred in tropical and subtropical regions. To dry the seaweed the algae/seaweed is spread on the nearby rock/shore and sun and air dried mostly within a day and has moisture content between 10 and 15%. Collected and stored, milled as feed for pyrolysis conversion.
Hydrothermal processing is developed as a technique for use in wet organic biomass and as such difficult to be used for direct in combustion. Through hydrothermal conversion able to accelerate the planet's natural processes and provide the high pressure and temperature environment required to convert these organic wastes into products with a higher energy density, cleaner fuels similar to a lignite coal (green coal), petroleum (bio crude) or natural gas (syngas).
Since the application of sustainable technologies for energy, including the efficient conversion of solar energy to electricity or hydrogen, might take longer than is expected, the development of alternative liquid fuels has been considered a key research area in the last two decades. Shifting the production of carbon-based chemicals produced from fossil fuels to renewable raw materials and as such part of the drive for or of sustainability. Experiments in hydrothermal processing have demonstrated the potential for upgrading wet biomass, through carbonisation, liquefaction and gasification, to yield products with a far higher energy density than the original material. Commonly available feedstock's for this system could include food waste, manures and sewage sludge, and include the use of fast growing algal biomass to produce third generation biofuels. Creating ideal or optimum processing environments bio fuels for the aviation sector conversion of algae to bio fuels & chemicals microwave pyrolysis/extraction.
Algae and seaweed can be reduced into bioactive compounds and fuel using hydrothermal conversion or liquifiqation wit a high moisture content being between 80-85%. Applicable when outside drying using sun/air is problematic due to high moisture contents as is often the case in cold and temperate sea climates re and the hydrothermal process the favoured option.
Availability of enough and low cost energy is essential to any developed civilisation and in fact there is a direct and proportual link between availability of energy and development and lifestyle of a civilisation including its war machinery on the other. The development of the liquid fuel-based transportation system was perhaps one of the most important and enabling technologies of the industrial revolution currently.
Try too imagining the fuel delivery/distribution and the solid/liquid waste collection/removal problems of a major city of several millions using donkey and horses for transportation. The fossil-fuel-based transportation fuels such as gasoline, diesel, and kerosene are liquids, which can be easily stored and distributed, and the final end products of their combustion, carbon dioxide and water readily dispersed in the environment as such. Bio fuels produced from renewable biomass are the sustainable energy resource with greatest potential for CO2 neutral production/usage.
Similarly, the production of electricity from fossil fuels is convenient, because it can respond readily to rapidly changing energy demands.
Fossil fuels are been used either directly, to generate electricity, to improve the quality of life in general, for controlling the temperature in houses, travelling, the working places, refrigeration to store and maintain the quality of foods. While it is difficult to predict the exact date of the depletion of fossil fuels, the scarcity is one by now, transition to renewable resources should therefore be accelerated resulting in the frequently and unexpectedly changing political/economical environments, limiting access to and rising costs of the main fossil fuels.
There is no reel shortage of energy as stored in biomaterial but the energy density is low and cannot used as such without an upgrade or concentrating it. One way to solve this problem is the conversion of this feedstock into liquid fuel. These liquids have a higher energy density and are easy to store and transport and the needed infra structure in place.
A sustainable and profitable bio diesel production from micro algae is possible. This second-generation bio fuel can overcome the energy and environmental needs by integrating the technologies. Large quantities of algal biomass needed for the production of bio diesel could be grown in photo bioreactors combined with photonics and biotechnologies.
The direct hydrothermal liquefaction is energy efficient technique for producing bio diesel from algae without the need to reduce the water content of the algal biomass, which is in average about 80%.
Hydrothermal Liquid faction (HTL) also known as thermo chemical conversion from algae and these reactions take place in sub-critical conditions in a watery phase, avoiding the latent heat of vaporisation at high pressure/temperature. Cost-effective microwave assisted hydrothermal liquefaction is the latest novel processing route of algae biomass and provides a no enzymatic route for depolymerisation of biomass into sugars that can be used for the biological production of fuels and chemicals. After conversion of wet biomass which a high water content into liquid factions they can be separated using different and almost most of the known technique. Process can produce bio-crude from the non-lipid fraction of algae.
Basically there are two different routes to produce algae based crude one called dry-milling and pyrolysis and the other wet-milling and processing using thermal critical water or htl. The dry-milling (or dry-grind) process is the main process for producing bio-crude, carbon and gas.
In the htl process results in bio-crude and various by-products dissolved in water including sugars. By separating into various fractions, which allows for the production of organic substances and industrial products including ketones, acetones, starch, proteins, fructose, oil and ethanol.
Because the water does not have to vaporize it is from the point of energy consumption better than other processes. However more work still has done on different low energy type separate techniques like use of membranes, centrifuge, chemicals, participation by altering ph, oxidation, use of acids, electrolyse, microwave etc.
Integration at the source
To be used are combined with power plant like coal or using fossil fuel. Adding the co2 produced by burning the fuel will enhance the growth of the algae and being a nutrient. It includes a micro algal production at thermal power plants for sequestering CO2, wastewater treatment and emission control, integration of an internal heat exchanger network and utilization of high pressure and high temperatures from the conversion reactor for power generation. The residual biomass from oil extraction could be used to produce different chemicals and as source of small amounts of other high-value micro algal products. Under current EU regulation it cannot be used as animal feed without testing. However the Scarification of algae at a much lower temperature and pressure can be an alternative. Less than 120 degree centigrade and with in sterilisation processes.
Another exciting reason about micro algal oil or bio-crude is the potential of chemically converting it into kerosene, the basic component of jet fuel. Jet fuel now accounts for about 8% of the petroleum use with very few renewable alternatives. A few companies are already underway to achieve commercial-scale. Analysis of the energy consumption ratio (ECR) also revealed that for wet algal biomass (80% moisture content), HTL is more favourable (ECR 0.44-0.63) than Pyrolysis (ECR 0.92-1.24) due to required water volatilisation in the latter technique.
Research done in the US and England indicates that at optimum thermo chemical liquefaction (TCL) the yield was 39.9%. ? Carbon conversion efficiency for most TCL runs were >93%. ?
Bio crudes obtained at 350–380 °C had fuel properties close to petroleum crude.
A maximum bio-oil yield of 25.8% is obtained at a reaction temperature of 360 °C and a holding time of 50 min using 5% Na2CO3 as a catalyst. The bio-oil is composed of fatty acids, fatty acid methyl esters, ketones, and aldehydes. Its heating value is 30.74 MJ/kg. The bio-oil product is a possible eco-friendly green bio fuel and source of carbon-chemicals.
Bio crude productivity was highest for marine Derbesia (2.4gm-2d-1) and Ulva (2.1gm-2d-1), and for freshwater Oedogonium (1.3gm-2d-1). A range of model biochemical components, micro algae and cyan bacteria with different biochemical contents have been liquefied under hydrothermal conditions at 350 °C, ~200 bar in water, 1 M Na2CO3 and 1 M formic acid.