Site Navigation Links : Please click on SITE MAP
Biomass and Biodiesel
Biomass
Biomass is a rich resource of carbon material which can be incinerated to produce heat - wood, straw or even cow dung for fires or house-hold waste for incineration plants in urban areas. These are renewable forms of energy in that the source of biomass material is from crops that have turned sunlight into plant-life.
This subject area of Biomass is vaste and the text "Renewable Energy Resources" by J. Twidell and A. Weir has a chapter devoted to Biofuels. In this section only two aspects will be highlighted, namely, anaerobic digestion and biodiesel.
Digesters
If organic material is allowed to decay by bacterial action in air we are all aware that it breaks down into simpler organic matter and this is the act of composting. If there is NO oxygen present (anaerobic conditions) different sets of bacteria are brought into action and methane is produced. So a digester is simply an apparatus which allows biomass to decay under anaerobic conditions. The simplest equation to describe the process is
C6H10O5 + H2O = 3 CO2 + 3CH4
Thus carbon dioxide and methane are produced from the reaction of cellulose and water.
Although somewhat dated, the text by Peter-John Meynell "Methane : planning a digester" , Prism Press, 1976, gives a good starting point. Several small scale digesters are discussed and many hints and tips are provided.
Wikipedia provides another source of information at their site.
See also Telegraph, 16th June 2009, "Human sewage to power thousands of home" - article by Murray Wardrop and Engineering and Technology magazine, "More gas than wind" - article by William Knight issue 11, 21st June - 4th July 2008, www.theiet.org/engtechmag Also the in same magazine there is an article by Juan Pablo Conti regarding a farm methane plant - 20 June - 10 July 2009, Vol 4, Issue 11.
Since there is extensive literature on this topic further discussion will not be included on this page but references are given on-line at
https://sth-se.diino.com/f.thompson/migrated_data/EandH
A Defra article "anaerobic digestion.pdf " gives a general introduction
Sewage_Methane1.pdf is an article concerning digesters for sewage installations.
A manufacturer of digesters is given at www.biogas-nord.de
Description of an installation at Lowbrook Farm in Dorset.
Note - as with any flammable gas there is always the risk of explosion so digester installations must have adequate gas detection systems. Also, the gas can accumulate in "pockets" as it is heavier than air. It is with saddness that a fatality was reported at Lowbrook Farm from methane inhalation so site workers will need to wear protective masks in danger area.
Of all the popular student projects in my time of teaching at Manchester Polytechnic, building a digester ranked NUMBER ONE by an easy margin. A project at MSc level had been carried out in the mid- 1970's (see page 120/ 121 in Meynell's book) but the experimentation was a little complex. Therefore a simple digester was designed to be "student friendly". This is shown below:-
An oil drum with the top removed acted as a container for the source material, namely, cow manure. This was mixed with water (50:50 mix) so there was about 100 litres of starting material. One hundred litres of liquid (the "seed" material with anearobic bugs present) from a digester at Davyhulme site, Manchester was added and an inverted dustbin provided an effective gas holder. There was a small gas loss round the periphery of the dustbin but this presented no hazard in a well-ventilated room. The container was heated to approximately 35 degree C by wrapping an electric blanket around the drum. With the gas tap turned to "off" position, the ingredients in the apparatus started their fermentation process and from time to time the liquid was stirred to stop sedimentation. The student's exitement at seeing the gas holder start to rise, indicating gas production, was always a delight; and this usually occured after 24 to 36 hours after mixing.The weight of the gas holder maintained a gas pressure of about 2 inches of water. When the holder had reached its extremity that gas was burnt off. Combustion using a bunsen burner needed a gas pressure of approximately 5 inches of water so household bricks were loaded onto the top of the dustbin causing it to move to a lower level and so compress the gas. The gas tap was opened and the bunsen ignited - a gas supply par excellence. Further invistigations were sometimes made to assess the quality of the gas and remove carbon dioxide ("scrubbing" - Meynell, page 75). Other parameters of the liquid waste ( pH and viscosity) could also be monitored.
The "seed" material is important in that gas production is obtained within a fairly rapid time scale and so maintains the student's interest. Cow manure does contain the necessary bacteria but only at low concentrations and the gas evolution would only occur after two or more weeks if the "seed" was not added.
The above apparatus is, clearly, a batch unit so that the gas supply will run out after a short time and the apparatus will then require emptying and refilling with new material. For commercial digesters there are facilities for contiually replenishing the source material and removing "spent" material; this is called a continuous-process digester and, importantly, a continuous supply of gas is then available from the digester. Simple units like the above were used by countries at the time of War when fuel was scarce and expensive, perhaps future fuel shortages will see their return.
Biodiesel
As petroleum reserves in the world will become depleted at some point in this current century, attempts are being made to develop alternative fuels which can take the place of petroleum based fuels. Throughout the world any fuel for transportation offers the biggest challenge as the energy density of vehicle fuels must be large. Hybrid vehicles go some way towards making our use of fuels more efficient and page 21 suggests that a long term strategy may involve fuel cells with a totally new Hydrogen Economy. In the immediate future, however, Biofuels give another route to fuel diversity which offers promise for the motorist http://en.wikipedia.org/wiki/Biofuel
Production of biodiesel is but one small segment in the field of biofuels. In very approximate terms it started in the early 1990's and tax incentives were given in Europe to make it cost competitive with mineral diesel. In the UK there was little development as fuel duty had to be paid on biodiesel at the same rate as ordinary diesel. It is therefore notable that our European cousins have a big lead on their UK counterparts in biodiesel. Since 2007, however, the government has allowed biodiesel to be produced for personal use up to a limit of 2500 litres per annum without paying any duty and therefore there has been a marked interest in UK for this fuel in the last year.
The chemical reaction for deriving biodiesel from vegetable oil ( termed
transesterification ) is given schematically below where ME is the methyl
radical and R represents a triglyceride functional
group
The most commonly used catalysts used for the transesterification reaction are NaOH, KOH or H2SO4 .
Several analytical methods have been used to monitor the progress of the above reaction and detect the final purity of the biodiesel::
Nuclear magnetic resonance (NMR), Gerhard Knothe, (2000) Journal of the American Oil Chemical Society, Volume 77, p489
Infrared spectroscopy (IR), R. Alcantara et al (2000) Biomass and Bioenergy, Volume 18, p515
Chromatography, K. Kanisa (2008) European Science and Technology, Volume 110, p422
One can therefore be assured that the process of producing biodiesel is well understood and a recent European Directive envisages that by 2010 diesel fuel should be made up of 5% biodiesel.
Making one's own Biodiesel
With the recent relaxation in fuel duty in the UK for personal fuel use it is tempting to make biodiesel at home on a domestic scale. If one can obtain used oil than so much the better as the final fuel cost per litre will be significantly less than pump prices.
Kits for little over £1000 are available which will, typically, produce 100 litres in a batch process. So, with about 20 "brewing" sessions per year, one's average motoring fuel needs would be met. (See www.vegetableoildiesel.co.uk or
It is advisable, however, to dabble in a little chemistry before investing relatively large amounts of money in a kit; that is, one would be advised to try to make biodiesel on a small scale in the kitchen. Used oil can be obtained from the chip pan and the other chemicals were purchased by the author from a local supplier - KOH and methanol from www.trinity-research.co.uk.
PROCEEDURE - this was taken from "make your own biodiesel" http://journeytoforever.org/biodiesel_make.html - - please take note of safety advice in this document .( this document has been placed on https://sth-se.diino.com/f.thompson/migrated_data/EandH for your convenience )
(1) Preheat 1 litre of oil to 55°C - oil in a metal container in a bowl and pour boiling water into bowl
(2) Mix by hand 5.5 grams of KOH in 200 ml of methanol in a jar with a swirling motion - this takes about10 minutes and allows the oil to heat up (stage (1)) in its water bath.
(3) Oil transferred to a 2 litre glass jar .... Methanol/ KOH added to oil .... stir for 30 mins just to make sure reaction reaches completion. The setup is depicted on page 12 of the article and a small heater, a therapeutic heat pad, was wrapped around the jar to avoid heat loss. (stirrer , in the present case, was a electric drill with a paddle secured in the chuck - the drill speed was controlled by a 1.2 kW Maplin controller part LP41U and the speed range could be varied between full speed and zero rpm)
(4) This mixture is tranferred to a separation funnel and one allows about 5 hours to settle. An illustration of the separation of biodiesel from glycerin is shown below:
A well marked division is very obvious and a tap at the bottom of the vessel allowes the liquids to be decanted separately. The biodiesel needs to be washed to extract small inpurities as the final stage ( stage (5)). It is unlikely that NMR, IR or Chromatography analysis will be available in the kitchen so two simple purity tests are usually carried out:
Methanol test - add 3 ml of biodiesel to 27 ml of methanol in a small bottle - shake for 20 seconds and allow to settle --- if the liquid remain clear then one can assume that the conversion process has been taken to completion -- if small globules appear at the bottom of the bottle then there are free fatty acids, FFA's, present and further transesterification is required.
Water test - add 50 ml of biodiesel to 50 ml of water in a glass jar - shake for 20 seconds and allow to settle --- the liquids should separate within a minute or so.
With tests on the biodiesel being successful one can be assured that it is ready for use BUT FIRST CHECK THAT NO DAMAGE WILL BE DONE TO YOUR VEHICLE.
Summary
Whether or not micro production of biofuel is to your taste it must be said that using waste products to produce biofuels has a double gain . Firstly, it avoids the initial problem of getting rid of the waste and, secondly, it produces a usable product; in many respects it is akin to composting household waste.
| Index Page | Top of Page Next Page |