An attractive approach to converting biomass into liquid or gaseous fuels is direct gasification, followed by conversion of the syngas to final fuel. Ethanol can be produced this way, but other fuels can be produced more easily and potentially at lower cost, though none of the approaches is currently inexpensive.
The choice of which process to use is influenced by the fact that lignin cannot easily be converted into a gas through biochemical conversion. Lignin can, however, be gasified through a heat process. The lignin components of plants can range from near 0% to 35%. For those plants at the lower end of this range, the chemical conversion approach is better suited. For plants that have more lignin, the heat-dominated approach is more effective.
Layout of a Typical Biomass Gasification Plant
Once the gasification of biomass is complete, the resulting syngas or synthetic gas can be used in a variety of ways to produce liquid fuels as mentioned below
Fischer-Tropsch (F-T) fuels
The Fischer-Tropsch process converts “syngas” (mainly carbon monoxide and hydrogen) into diesel fuel and naphtha (basic gasoline) by building polymer chains out of these basic building blocks. Typically a variety of co-products (various chemicals) are also produced.
The Fisher-Tropsch process is an established technology and has been proven on a large scale but adoption has been limited by high capital and O&M costs. According to Choren Industries, a German based developer of the technology, it takes 5 tons of biomass to produce 1 ton of biodiesel, and 1 hectare generates 4 tons of biodiesel.
Syngas can also be converted into methanol through dehydration or other techniques, and in fact methanol is an intermediate product of the F-T process (and is therefore cheaper to produce than F-T gasoline and diesel).
Methanol is somewhat out of favour as a transportation fuel due to its relatively low energy content and high toxicity, but might be a preferred fuel if fuel cell vehicles are developed with on-board reforming of hydrogen.
DME also can be produced from syngas, in a manner similar to methanol. It is a promising fuel for diesel engines, due to its good combustion and emissions properties. However, like LPG, it requires special fuel handling and storage equipment and some modifications of diesel engines, and is still at an experimental phase.
If diesel vehicles were designed and produced to run on DME, they would become inherently very low pollutant emitting vehicles; with DME produced from biomass, they would also become very low GHG vehicles.
Biodiesel, a petroleum-based diesel alternative produced by transesterification, works as efficiently as the commercially sold diesel and hardly requires any changes in the engine. For those who don’t know, biodiesel can be produced using any oil derived from plants such as soybean oil, cottonseed oil, canola oil, etc. or from animal fats, like beef tallow and chicken tallow.
Over the past five years, due to the spike in fuel prices, people have started moving towards energy independence and have started small private biodiesel production units. According to reports, biodiesel made from useless tires could solve fuel security problems. Tires are a big problem as they create a lot of waste. We can turn this waste into useful oil and help not only the environment but also the economy.
If you are new to biodiesel production, some of the crucial things to know are:
This should not come as a surprise, safety rules are necessary to avoid the contamination of soil and water resources, fires, and personal poisoning.
Vegetable oil to biodiesel conversion requires methanol and lye. Both these chemicals are extremely dangerous since they are not only inflammable but can also cause neurological damage in case of excessive exposure.
A number of biodiesel related accidents and fires have been reported over the last few years. The incidents were a result of pure neglect. Some of the safety measures you should never forget to take are:
Don’t process inside your house.
Don’t keep any oily rags in the vicinity, they are the main source of spontaneous combustion leading to huge fires.
Don’t use paint stirrers or drills to mix up the biodiesel. It can cause a fire.
Don’t use blenders to make test batches, the ingredients can react with rubber seals.
All hazardous and dangerous products should be kept in an approved metal fire cabinet when not in use.
2. Environmental Regulations and Feedstock Collection
Currently, non-commercial and small-scale biodiesel production areas are not subjected to regulations by the Department of Environmental Protection (PADEP). However, if complaints or problems arise due to your biodiesel product, your plant might be subjected to discretionary enforcement. Moreover, you’ll need approval if you wish to increase the size of the production unit.
The disposal of by-products, on the other hand, requires the approval of the PADEP and should be done based on the latest guidelines. These guidelines can be obtained from your local Department of Environmental Protection.
Apart from following the rules and regulations, the availability of feedstock is crucial for the process.
One gallon of biodiesel requires at least one gallon of feedstock oil. To reduce production costs and to prevent food for fuel conflict, using inedible oils as a major source for biodiesel production is advised.
Usually, feedstock and feedstock oil are difficult to obtain, hence pre-planning is the key to produce the required amount of biodiesel on a regular basis. The collection and transportation of feedstock including used cooking oils are regulated by PADEP.
3. Time Commitment and Cost Requirements
New users usually underestimate the time requirements for proper and regular biodiesel production. While planning your biodiesel plant, make sure you allocate enough time to maintaining the equipment since improper maintenance lead to accidents. Feedstock collection and fuel processing also require a lot of time.
Other time-consuming tasks include handling and securing chemicals, air drying and water washing the fuel, testing the duel quality, and disposing of by-products.
Even though the cost requirements per gallon of biodiesel fuel process are much lower than the commercially sold diesel, there are a few things you need to take into consideration beforehand.
A detailed analysis of input costs versus the resultant value of fuel produced needs to be performed. The analysis should also include labor costs.
Investment in equipment and facility, feedstock transport and acquisition, chemicals, energy used and by-product disposal costs need to be accounted for as well.
4. Handling and Disposing By-products
During the production process, a considerable amount of crude glycerol is produced. Other processors that use water for biodiesel purification produced two gallons of waste for every gallon of biodiesel.
Handling this amount of waste can be taxing. It needs to be compliant with the PADEP rules and regulations. This not only requires more time but capital as well.
The crude glycerol by-product has 25 percent methanol as well as some hazardous waste. Converting it into marketable glycerin is not feasible on a small-scale since the evaporation of methanol cannot be contained.
The land application of methanol and glycerol are prohibited by PADEP. The disposal options from crude glycerol including methanol are:
Disposing of in a landfill.
You have to get special permission from PADEP for all the above processes.
5. Fuel Quality and Storage
Commercial testing of the fuel quality can rip you off since one batch can cost anything between $1000 and $1500. However, simpler fuel testing techniques like sediment testing, methanol testing, water content, viscosity, and cloud point testing can help you find a rough estimate of how good or bad the fuel is. These tests can also help you in finding what needs to be improved during the production process.
To store the fuel, use proper, biodiesel approved and rubber free containers. Using in-line filters while pumping the fuel in storage containers is the best practice. Usually, biodiesel produces use of 10-micron water-blocking filter or a 1-micron filter.
Petroleum approved containers also work well for storing biodiesel. Once in containers, the fuel should be kept in a dry, clean, and dark environment.
If you plan on storing the fuel for a longer time, using algaecide or fungicide additive is recommended since biodiesel is an organic liquid. Also, during cold seasons, the fuel gels, hence, blending in petroleum or anti-gelling additive is pretty important.
For best engine performance, you must use it within six months. If you can, limit the storage time to 3 months in warm and humid weather since the fuel can develop algae or fungus.
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