Sunday, May 23, 2010

4 phases of methanogenesis

The biogas is a major product of biogas plant. Most is burned in the cogeneration unit and receives the electrical energy and heat.

The biogas is generated by the bacterial activity without access to air. The Fermentation involves different types of microorganisms.

We can divide whol process into 4 phases:

1. Hydrolysis - in the environment is still oxygen in the air. Polymeric organic compounds (polysaccharides, fats, proteins) are broken down into simpler monomers - alcohols and fatty acids, releasing hydrogen (H2) and carbon dioxide (CO2).
2. Acidogenesis - consumes the remaining oxygen in the air and creates the anaerobic environment (without oxygen). This phase is made by viable microorganisms in the environment with or without oxygen. This creates higher organic acids.
3. Acetogenesis - with help of bacteria are more organic acids and alcohols transformed to acetic acid, H2 and CO2.
4. Methanogenesis - final stage of degradation process. Bacteria are strictly capable of life only in an environment without access to air, acetic acid decomposes into methane (CH4) and CO2. Some strains produce methane from CO2 and H2. This final phase is about five times slower than the previous three phases, so the size of the fermenter must be adapted to dosage of starting materials.

The resulting biogas is essentially a mixture of methane and CO2, which contains impurities such as N2, H2S, NH3, H2O:







NameChem. formula%
MethaneCH440-75%
WaterH2O0-10%
Carbon dioxideCO225-55%
Others-0-10%


The most problematic chemical is hydrogen sulfide (H2S), because if it is in a quantity over 0.1% it is corrosive to engines and technological equipment. Ammonia (NH3) is a source of odors. The presence of CO2 in the biogas is a benefit if the biogas is burned in cogeneration, CO2 acts as if the anti-knock in internal combustion engines.

Thursday, May 20, 2010

Heating in winter

How to make energy-independent house with the advent of winter each year, beginning each survey as it could save on heating as they easily survive the winter to reduce heating costs in the ever-increasing prices for energy? Of course, this question makes me not sleep. While the ideas may be enough and perhaps those that would be feasible, yet their implementation is needed funds and also some significant level of skill. And there is the question - can I make it?

In general, the answer is very simple. Put some solar collectors - but for the winter? So we can build a wind power plant - or large or small hydroelectric power plant, ... Such responses are interesting, but they can't save energy. First we need to say location where the house is situated. Where we want to build own power. We do not have any house in the valley, which is enough water in winter and freezes. Not everybody can build a wind turbine - because the neighbors would say. The sun is not much, even though they live on in the winter and sunny days.  

One suggestion, a little fantasy is a small construction equipment, which is based on wood gas or biogas. The skilled engineers / turner, welder, etc... for them it is not a problem to produce wood gas generator. And such a generator can make electricity from the combustion gas. There is a big problem, because it is not a classic addition gasifier as we know from cars. So the output we will have are electricity, and the residual heat - it will put a relatively large reservoir. From here we can provide heat for house and hot water. And the generator can reduce consumption of electricity from the grid.

Biogas - first try

My first attempt was in the PET bottle, but it did not last a higher pressure of biogas and PET bottle exploded. Luckily it happened outside in the garden, not inside the apartment. Advised that pressure in the generator is obviously great, so I made a mini generator instead of a glass container with a lid on the thread. The lid was metal, so I drilled a hole into it and solder copper tube. Generator shoul  be able to stand on the lid, I used more cork stopper that I stuck to the lid. I bent the tube and pushed into the cut PET bottles. Hole I thoroughly sealed with silicone adhesive. PET bottles I tested the water and made a tight fit. I poured water and made into small jars, which went to freely insert snip PET bottles. It was a matter of collecting bottle to leave no air. Methane is lighter as the air and mixed with air is highly explosive. Never light first developed biogas! May contain air and lit an explosion!

What is it feeds.

On the first attempt, I gathered poultry manure, which I have filled one-third liter PET bottles. I also added the same amount of cut grass. Everything was poured by rain water about 1.2 liters. All shake thoroughly and put in a warm place. Already in few hours it begins to ferment and develop its own gas. Once again highlights the danger of explosion during the first ignition of gas. We can use this PET project aj base for a large generator, but several times each day we should to free excess pressure in the bottle. Otherwise,thread PET bottles may explode. Large generator will be feed from kitchen waste, potato peelings, food leftovers but also if the old paper cut or picked into small pieces. Furthermore, all the waste of plant origin!

Pitfalls of anaerobic digestion

Gas appliances are designed for the combustion gases under constant conditions, is fed into the burner air (oxygen), in the case of methane (CH4) ratio of about 8 cubic meters of air per 1 m3 of gas. This design ensures the correct ratio of the burner of the appliance (stove, heater, or boiler), but also requires a constant pressure of gas (methane at about 200 mm water column).

Homemade appliances often lack the very important aspect - safety relief valve, which prevents the rise of pressure above the safe level. Therefore, described the explosion ....

The pressure required will ensure open hose, connected to a tank of gas (ie gas holder) and submerged under water 200 mm deep .. hose would work well as a safety valve - blows away the excess gas into the atmosphere.

Several years ago I had seen a description of a small gas works, designed for the use of natives in Africa, performance was perhaps 3-5 m3/day. More energy-efficient than wood burning in the primitive fireplace.

Gas could be implemented as a plastic bag, and could be inappropriate to restrict the oxygen in the gas at the rotting process.

ATTENTION! ATTENTION! gas is very dangerous medium, ATTENTION!

Wednesday, May 19, 2010

Disadvantages of anaerobic digestion

What can be better than have your own gas station? There is enough grass or other manure. Cows on pasuture are walking gas stations...But

note of any significant hazards lay experimenting with fuel gases. Gas is extremely dangerous, mainly because the next molecule compounds that burns (CH4), are located in close proximity oxidant molecule (O2). Combustion of such mixtures is a blast. 

It will take place in a split second, immediately raise the temperature of flue gas (gas formula PV = Rt), this leads to a large increase in volume or pressure in an enclosed space and the destruction of the structures. Such an explosion destroyed bridges, cut up houses, maim and kill people. Therefore, all gas equipment must be operated in accordance with applicable regulations. Equipment subject to regular checks and reviews, without them it is their operation illegal and punishable.
When somebody wants to experiment, whether they do so somewhere in the open, not in an apartment house or perhaps the basement!