QUESTION FROM THE FIELD: field testing of biogas

Posted by Gordon Hirst to Energy, 17th November at 10:18 PM

I am engaged in a couple of biogas projects in Laos and have had some marked success running 10.5 hp single cylinder Kubota diesel engine on biogas.

See http://erawan-biogas.blogspot.com/

As outlined in this blog, one of the variables which may have a significant contribution to the success of the test was the quality of the biogas.

Over the last year I have been looking for a practical way of doing a qualitative field test of biogas with little success. I have tracked down a hand held device made in the UK which looks as though it is the best thing on the market

http://www.edie.net/products/view_entry.asp?ID=3809&channel=3

However the GFM 400 starts at £3500 (GBP) so you can understand my reluctance.

I have been thinking about setting up my own field test however before I attempt this I thought I’d pass the word out:

1. Does anyone know of an existing test that I could adopt

2. Would appreciate anybodies input into such a device,

I am thinking of a known size reservoir, known (standard) pressure, a nozzle of known size and a burn and count time. This could be done with a PET bottle and a cheap pressure gauge. The thing is this is a qualitative test rather than a quantitative test and will only have value when compared to other similar tests.

any feedback would be good 

gordon hirst

gordon_hirst2004@yahoo.com.au 

 

 

 

 

Posted 8 Months ago by Gordon Hirst

The following is a report I have just published following the success of the biogas/diesel project at the RTC in Laos
I will attempt to upload the pictures and video in the next few days

Running diesel engines on biogas:

Synopsis:

This document covers technical details and information gained during experimental work on running a small diesel engine using biogas produced from a cow manure biogas digester.

Background:

In May 2008, a 10 m³ fixed volume digester was installed at the RTC (Rural treatment centre - Hospital) located at 45 Km of the Laos Capital, Vientiane, 5 km from Road 13 North(1,2).  The biogas is primarily used for cooking in both the doctors’ house and the hospital. However the remoteness of the site meant that it is “off grid” and they relied on a 10.5 Hp diesel engine driving an old generator for power, it was speculated that the biogas could be used to power the generator, thus relieving the hospital of some of the burden of the cost of diesel fuel.

Technical data:

The bio digester is a 10 m³  fixed volume construction (3) therefore relies on the anaerobic digestion and the domed shape of the roof to create the pressure. The Digester is fed with 100kg cow manure and 100 Litres water every morning. It could be said that, since the installation, the RTC have had some issues with the digester and it is not running at its optimum capacity (estimated about 40% - 50%) and the volume of gas (and hence the pressure).Also the quality of the biogas does vary depending on conditions, IE: heavy rain reduces the capacity significantly. On a good day 17 Kpa of pressure can be achieved.

Questions have been raised over the chemical make up of the biogas and its relative quality. At this stage without any suitable test equipment, is very difficult to assess, but it does seem to vary again depending on atmospheric conditions.  A guess would put the methane component at about 50 %, the others being made up of water vapour, sulphur, Co2 and others.

 

Tests:

Test 1

January 2009

The initial tests were undertaken on the RTC’s diesel engine where an adapted air filter housing with a hose connection for the biogas an a ball valve( see picture 5). The generator was disconnected thus having no load. The condition of the engine is poor, they do no charge the air filter with oil and the fuel filter does not work. It is impossible to say what the compression ratio is, at a guess it could be as low as 13:1 or even 12:1, the result of this is the stoichiometric ratio is achieved a lot later in the stroke.

As mentioned before the quality of the biogas is undetermined, however there was a lot of water in the feed pipe which was resultant of condensed water vapour. The pipe needed to be drained for several minutes before attempting the test. The gas pressure was indicated at 12 Kpa. (1.7 PSI/ 50 “H2O)

The Engine was started on 100% diesel and ran for a few minutes and the valve on the air filter slowly opened to allow the ingress of the biogas.

The engine immediately spluttered and died. This was repeated several times the engine did not pick up on the biogas at all.

Test2:

February 2009

(See picture 10)

After some deliberation it was decided that the introduction of a mixing chamber could possibly help the combustion process. Methane particles and much smaller than air particles and hence would be required to be mixed prior to draw into the cylinder. (See pictures 6 to 10 ). The mixing unit consisted of a of a sealed chamber of approx 4 litre capacity split by a ‘nozzle’ plate ( a stationary impellor) with the gas inlet and valve in the upper chamber.

 The gas line again had to be drained of water prior to the tests. The indicated pressure was 10 Kpa.

After initially starting on diesel the valve the biogas was introduced. It was noted that the spluttering and engine fade occurred at a specific point; the engine accepted the gas more with the mixer.

Another interesting observation was the change in the colour of the smoke when the valve is opened to let more biogas in (grey), then closed suddenly (black). 

It is understood that the likely reason for this is the oxygen starvation caused by too much unignited biogas. The slowing of the engine causes the rack to be pushed to the end of travel increasing the diesel fuel input. The rapid closing of the biogas valve causing the increase in speed and the burning of excess diesel fuel, hence the black smoke. Ref: www.erawan-biogas.blogspot.com)

At a stable position of the biogas inlet (IE: just before spluttering and engine fade) we conducted a test to ascertain the ratio of biogas/diesel being used.  This was achieved by rigging up a 100 cc plastic syringe which was filled with diesel fuel; the injector return line was also fed back into the top of the syringe.  A time was taken for a known quantity of fuel to be consumed. This was repeated without the biogas.  

Result:  Ratio 15-20% biogas / 80% - 85% diesel.

Test 3.

November 2009

(see picture 14)

For the next test it was decided the only logical next step would be to try to improve the quality of the biogas. For this a crude filter was constructed using a 20 litre plastic bin filled with soaked wood chips. The bin was fitted with an inlet and an outlet connection which consisted of holed pipes which protruded though the bin and wrapped in sponge to keep the woodchips out of the pipes.

(See pictures 11 to 13)

Unfortunately this visit ,the Doctor sad he was unwilling for us to use his engine in tests, unbelievable the engine is now in a worse condition than in February. 

An alternative engine was sourced this time an 11 hp Kubota diesel single cylinder. In good condition which had been used previously to run on bio diesel from Soya.(4) Because of this the engine was already equipped with a set of four off 100 cc syringes mounted in a frame above the engine. The diesel engine is on a bed integrated with an Onan 3 KV power plant driven through a duplex pulley with a 130:90 ratio. The generator remained in place for the duration of the test. The output power was not connected.

Because of the mass of the bed in total about 170 Kg. The unit was transported to the RTC on the back of a flat bed truck (Ute) where it remained for the duration of the test. The mixing unit utilised in test 2 was connected to the air intake of the engine.

The biogas was initially at 7.5 Kpa, the gas was dry (no condensed water vapour)

Test 3a. 100 % diesel running the diesel engine on 100% diesel , 46 seconds to consume 10 cc of fuel

Test 3b. Introducing biogas.

The most immediate response was an increase in engine speed.  The throttle was to reduced to that approaching test 3 a to try to reflect a true test however this was only estimated by ear.

3 minutes 36 seconds to consume 10 cc of fuel:  ration 80% biogas: 20% diesel

Test 3c. As 3b introducing the gas filter, unfortunately a reaction between the hose connections and the cement caused the threads to disintegrate, thus making a seal impossible. We could not conduct any further tests with the gas filter.

Gas pressure at end of Test 2; 2Kpa. Note the valve on the top f the tank had been turned off therefore the gas consumed in the test was the gas present only in the system. Also the gas had been utilised for cooking during this time.

 

Notes and conclusions:

 

1. From test 3 b it is concluded that a viable power source is capable using biogas however diesel fuel will always be needed for a. ignition and b. lubrication of diesel injectors. A literary search concludes that the optimum ratio for biogas/diesel fuel is 80:20.


2. The longer term issues of using biogas as source fuel such as the harmful effects of sulphur on vitreous products within the engine. This was one of the elements that the gas filter is expected to remove.  Commercial desulpherisers are available at low cost and could be sourced if required.


3. Biogas input control: As it is envisaged that the appropriate use of the biogas/diesel engine configuration is thought to be for power generation. In this instance control of output of the engine is critical as the biogas pressure will drop over a period of time.  There are numerous preliminary designs in progress for a cheap workable system; this would form stage 2 of the development.


4. Field testing of biogas:  It was recognised that the success of test 3 could be attributable to two variables. Firstly the superior condition of the replacement engine (higher compression) the second being the quality of the biogas. At present we have no practical way of testing the biogas .

 

Posted 7 Months ago by Colin Cockroft

Hi Gordon, I have a colleague who has done a bit of work with bio-gas systems and I have passed your field test question on to him, I will let you know if he has any solutions.

Posted 3 Months ago by Mark McNee

Hi Gordon,

Hope I'm not too late mate. November you post...

Marko here. Nice work mate, sounds like your kicking some goals there! Fellah, my 2c below from a reformed petrol head turned renewable fuel big engine intaller and tuner. Please feel free to call me a clown and get me to do something useful for you.

Mate I came from Landfill gas and 0.5 to 1MW Cats, and LNG and CNG over diesel in logistics and light vehicles and now work in large (>3MW equiv) recip compressors. So all good comp ratio engines, all turbocharged (which helps a heap for gas) rather than your awesome little single. The LFG kit is pretty, urm, agricultural, so I might share what I have learned from them.

I might just suggest you do a load test for tuning. If you want to pull it off its normal load (which Id suggest) you might be able to use a couple of pedistal fans and ~1kW bar heaters to stack up to your 60 to 80%. Old aircons also pull some load, see what you can find. Might be worth seeing if you can get an earth leakage power board for said loadbank though. It might be easy enough to do some load step and shed tests to similate what might happen in the hospital.

It depends on what you are looking to do, full gas conversion / gas over diesel / diesel over gas.  There are also 2 things you can mod to get some freebies; The engine itself, and the gas supply system. My 2c on both.

Ok, for the gas over diesel (>80% diesel),
Engine:
This will take the least mods apart from the petrol engine mentioned below. All the gas is assisting with here is to COMPLETE the diesel burn. It will give your little atmo (ahh, non turbo/super charged) plugger the best bang for your buck. All of the power is still coming from the diesel. It will give you similar performance improvements to a turbocharger, with much easier maintenance. Knowing that the power is still coming from the diesel, you have hit the magic number already, 80% of the normal duty cycle of the diesel injector is the BEST you can hope for with normal petrolium diesel. If you have some veggie oil, which has a much better comp ratio and burns colder, you can push it a bit harder. (Into the high 60%s I think)
Gas Train:
Must have: This is also a pretty easy mod. While perfoming the ones listed below will give you better performance, they probably wont pay for their effort or expence. All I'd suggest is that you regulate flow into the engine. If you give it a gut full to burn, it will just snuff. A ball valve is not ideal for this application, if you can find a small globe valve perfect, but a small length of small ID pipe would probably serve you best $/function.
Nice to have: A BFT (Urm, big something tank...) might be the best function/$.effort to drop out any condenced water and buffer any swings in the gas content. 30 secs of resonance would be massive if you can afford it, 5 to 10 secs would prob do what you need it to. BE VERY CARFUL THIS IS WELL SEALED, STAYS AT POSITIVE PRESSURE AND GETS PURGED OF AIR. It would be a nice little bomb if a carburetted mix of gas and air got in there...

Diesel over gas (80%< diesel <20%)
Ok, if you want to push harder than that; you can, but it is getting into "lean burn" territory, which is fine, but will need you to mod the diesel injection system. If this is done, it will no longer run effectively on diesel alone. So you had better have a reliable source of CH4 before perfoming mods like this. Without knowing the specifics of the unit you are on, it will just give the injector a different duty cycle, so if it is mechanical, which I'd expect it to be at that size, you may have to fiddle around with the linkages to to it to track with throttle / load.
Gas Train:
Must have: Now your gas is driving the engine, and the diesel is just acting as a "spark plug" for you. You will have to grab the nice to have from above (BFT and H20 control), but replace the small ID line from up there, with some form of butterfly throttle. This will have to be linkaged up to the droop voltage controller (or whatever actuates the diesel throttle) and will take some fiddling. It will have to simultaneously back off the diesel as well.
Nice to have: Without knowing the specifics of your fuel source, I can only take a stab. If you can get some JT cooling from a small pressure drop, you can use it to drop out some H2O, and while it will heat your charge slightly, you can also use Exhaust heat to change the dew point. It does help both from drier fuel, but it also heats the CO2 in the fuel stream that would otherwise waste combustion heat.

Gas engine:
Engine:
You will need a spark plug if you want to go under 20% diesel for your auto ignition, and Id say with small engines, its just not cost effective to mod the head unless you dig up a petrol gennie from somewhere. That is assuming you have a constant supply of gas. If you find one of those, throw the specifics back up on the site here and we can have a look at ignition timing, gas throttle specs and a startup sequence for you.
Gas Train:
You will need a long >30 resonance time BFT for this one. With only an air and gas butterfly mix coming in, it would not be fast enough to chase any dramatic swings in fuel quality. Dry it as much as you can. Combustion heat would be of concern, but not a deal breaker, just check it has plugs that can take it.

For full gas engines, on LFG installs we had to do on a shoestring, and gas conditioning is everything. It would be nice to have a GC, (gas cromatograph) but at a 1/4 Mil a pop, not the most feasible kind of technology. We monitored real time with a glorified calorimiter, that took the heating value of whats coming in. If you can get your hands on an old copper BOM Calorimiter, and grab some samples from different brews and note the temp of the sample when taken. You can assume most of the BURNIE stuff is CH4 and most of the NOT is water and CO2. You can split the C02 and water by doing an untreated test, then a test after you cool the gas, between known temps, measure out all of the water that comes out and you can work out if it was saturated. Coming back through LHV will be pretty easy from there. 

You will need to know the input heating value and the H2O saturation so you can tune the engine to get under that magical 20% number if you do come across some cheapie petrol gensets.

Hope this helps,
Rock on

Marko

Posted 2 Months ago by Gordon Hirst

Hi Marko

thanks for that would like to get in touch and 'chew the fat'
gordon_hirst2004@yahoo.com.au

cheers

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