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we’re working towards a native chp system built standard into the power pallet. the goal is to make available both the hot water from the engine cooling system, as well as the hot exhaust after the pyrocoil, towards off board heating needs. we’re working on liquid heat exchangers to produce hot water for heating and hot shower water. we’re also working on hot gas to gas exchangers so you can get hot air for fuel drying and ag crop drying.

there are many fancy ways to do this. bear will document these later. there are also some cheap obtainium ways to do this. here below are some of the cheap hacks you can do with stuff laying around the homestead.

1. burn the flare into a salvaged on demand water heater.

these on demand heat exchanger sections are surprisingly efficient. in the picture here we’re sending 800c flue gas into it, and you can hold you hand over the top of it without too much pain. i put a piece of crumpled paper down inside the exchanger and it didn’t catch on fire. didn’t even get fully pyrolyzed.

the water coming out is about 80c in this picture. bear is using it to pasturize some wood chips so he can grow mushrooms. yes, the eating type.

2. put the swirl burner down into a bucket of water. look at that blue flame!

this is darrel’s new gasifier hot tub heater using the standard gek swirl burner. it is using the standard gek type ejector with a elbow at the end so the feed pipe comes back up parallel to the burner. this makes it easy to put it down into a bucket. we should really add a longer flue on the swirl burner and get it even further underwater. but it works surprisingly well at the stock length.

as you can see, the water comes to a rather vigorous boil. the swirl motion motivates the hot gas to the heat exchange surface, minimizing the laminar layer.

for the brave, you can sink this right down into your hot tub. for the less brave, you can run a second pump moving water between this hot bucket and your hot tub.

these and other new CHP systems will be put to work this weekend at the APL holiday hot tub party. more info on that in another post.

We tested Darrel’s heater again last night.

We got ~30 gallons of water to a rolling boil in about 50 minutes.
A few folks were interested in how to use water to calculate energy input, I’ll show work below.

Using those numbers:
30 gallons * 3.785 L/gal * 1000 mL/L = 113,562 mL

The density of water is _very_ close to 1 g/mL:

113,562 mL * 1 g/mL = 113,562 g

A calorie (small c) is the energy it takes to raise one 1 gram of water by 1°C (at standard temperature, but this holds pretty well at other temperatures):
deltaT = Tfinal – Tinitial = 100°C – 15°C = 85°C
113,562 g * 85°C = 9,652,800 calories

One calorie is 4.184 Joules:
9,652,800 calories * 4.184 J/cal = 40,387,315 J

Coverting to kWh:

1 W = 1 J/s
1 J = 1 W for 1 second
50 min * 60 sec/min = 3000 sec
40,387,315 J / 3,000 sec = 13462.44 W = 13.4 kW_thermal (net)

We had a number of losses off the barrel, so with fine tuning the heat retained in the water could be brought up. Accounting for losses (barrel bottom conducting with concrete, sides radiating heat, steam evaporating from the water surface) probably brings the heat going into the water up to 15-20 kW .

The flue gas was still pretty hot off the top of the flare, so there’s more there to be captured as well.

In theory, the GEK should be putting out up to 40 kW thermal (total gas chemical heating value) for a 10 kW electrical system. If we fine tune a water heating system (eliminate or calculate the losses), we can get the raw gas heating/power value from a system without needing to run an engine.

Here is what jim identifies as a boat heat exchanger that we’re using to capture heat from the coolant loop of the engine. There are also a number of plate exchangers that are affordable, some in 3×8" form factors that should fit nicely below the radiator.

2 Responses

  1. Under “obtanium built for the job” file gas or oil fired tank water heaters (remove burner, deal with moving the heat so you don’t overheat the thing, point the flame (or post-flame exhaust) in the bottom and connect the stack to the top) and gas or oil fired boilers (or for you hot air folks that prefer not to pass though hot water on the way there, furnaces). A large thermal store (big insulated tank of hot water, usually not under pressure) is beneficial in absorbing heat as created and doling it out as needed, and a waste heat dump of some sort is pretty much a good idea. For steel boilers, a mixing valve to keep incoming water at or above 125F to reduce corrosion is also helpful.

    Often enough available cheap or even free when folks switch out an old unit – not so good if the old unit is rusted out, but many are not bad, or have problems in the parts (burners) you won’t be using.

    As ever when you start messing with water, heat and items that hold pressure, pay lots of attention to using temperature and pressure relief valves to keep things safe if you screw up, and control systems to keep from actually using those relief valves in practice. Steam explosions are Very Bad News.

  2. If using CHP primarily for power, with heat being a side bonus, there will be times that power is needed but heat is not — for example, if you’re heating a hot water tank, and it’s reached it’s maximum safe temperature. To avoid having more heat than you want, add a thermostat controlled valve which can bypass the heat exchanger, and send the exhaust straight up the flue without heating the hot water tank. This is vastly simpler than using a waste heat dump to cool off the hot water tank.

    If using CHP primarily for heat, with power being a side bonus, then the entire CHP system can be turned on and off by a thermostat… excess heat is less of a concern.

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