1 reply to this topic

[rexzietsman]

We are looking to build GEK's for rural electrification in Mozambique. We want to keep everything as simple as possible. As such, I am looking to control the GEK manually without using a GCU. For the purposes of this discussion, we can make some assumptions:

• there will be a full time operator looking after the unit
  
• we expect the unit to run about 10 hours per day
  
• the fuel will be coconut shell or wood chunks
  
• we envisage using a Nissan 1400cc petrol engine fitted with a syngas carburettor and a 12V cruise control to maintain speed

Once the gasifier is operating, the engine will determine the gas draw from the gasifier. As the electrical load will vary and the feed moisture and CV are variable, the amount of feed required is not fixed.

My question is:
Is there a method that we can employ that will allow the operator to measure the depth of the feed in the gasifier? The item that comes to mind is a rod with a flat bar on the end that can be pushed down until it reaches the bed. Once the depth is known, the operator can add more fuel if required. The issue that has to be addressed is that, ideally, we do not want a penetration into the gasifier as air can leak in where we do not want it to leak in. So, are there any ideas out there? I have thought of putting a non-magnetic stainless steel tube on the top of the gasifier with a steel rod inside that can be moved up and down with a magnet... I dont know how practical that would be though.

I also concede that measuring the physical depth of the gasifier is not necessarily the best way to go about it. I assume that the operator will be able to see the pressure drop across the gasifier from which he can infer what is happening inside. The major drawback of this inference is: what if there is simply a blockage in the gasifier giving a pressure drop that infers a high level when there is not?

I look forward to any suggestions.

[jimmason]

rex,

if you want to do this manually with an operator present, some poking bar from the top will be fine i think.  you can have this bar pass through a tube with a grease seal.  or pass through a tube larger than the rod, with the two ends capped and drilled to the exact dimension of the rod.  this reduces the amount of sliding surface to foul with tar.  and you can still pack it with grease.

you can also get electrical and use push switches like used in grain silos.  they are sensitive switches that trigger with the horizontal force of stacked fuel.  not vertical.

or you can do the spinning star wheel type thing that can only spin once the fuel drops below a certain level.

or, you can just use a temp switch.  as the fuel level goes down, the temp in the hopper tends to rise.  this is especially the case when the fuel drops very low and there is no new fuel to feed into pyrolysis or drying and thus nothing to consume heat.  there is quite a distinct temp spike at this point.  likely enough that some type of temp only analog switch could be mounted in the side of the hopper at, say, 6" above the reactor top, that would set off a buzzer or whatever you want to use for the "add fuel" signal.


what have you found with 12vdc cruise control that you think will be good for speed control on an automotive engine based genset?  

are you proposing to automate the mixture or leave that a manually tended endeavor?

thanks for the interesting question.

jim