Power from gasified waste

[Roger Feeley]

I'm always amazed at the breadth and depth of knowledge on the Creek. So here we go.

I'm looking into gasification. I found a number on the web that said that 1lb of municipal solid waste will produce 8546 btu.
I found a converter on the web that said that 8546 btu converts to 2504 watts.

BTU/lb of MSW = 8546 = 2504 watts

But I'm used to thinking of electricity in terms of a continuous flow. To me, that 2504 isn't the same as what I think of in an AC circuit.

How do I convert that 2504 watts from burning 1 lb of municipal waste into what I generally understand. Don't I have to stretch that 2504 over time in some way?

Put in a slightly different way, I can gasify 83.3 lbs of material per hour (1 ton/day). If I ran a generator, how many kw can I get?

[Grant Wilkinson]

I'm far from expert in this, but I believe that the heat you get from burning anything can only be converted into electricity by using it to make steam. The steam turns a turbine of some sort that turns a generator that makes electricity. There are huge gasification plants in Europe and that's how their process works. The heat required to produce the gas from waster is incredible! If the heat is not high enough, you produce smoke and ash.

I'll be interested in reading other replies here to see if there is another approach.

[Roger Feeley]

Grant, I think you are voicing my problem in a different way but you get it.

In a sense, I'm converting yards to mph. A yard is an expression of length and mph is velocity. I think I may have the same problem. a watt is a unit of energy and kwh is more like velocity or flow.

But I'm producing btu over time. Aw heck...my head hurts.

[Rod Sheridan]

The values I've seen range from 400 to 500kWh/ton of municipal waste.

If you burned 1 ton that would be the monthly power consumption of my house.........Rod.

[roger wiegand]

if a pound generates 2400 watts then 1 pound/hour will deliver 2400 watts/hour or 2.4 kWH (1 pound per 10 hours is also 2.4 kWH, 240 w/h x 10 h.)

[Roger Feeley]

The values I've seen range from 400 to 500kWh/ton of municipal waste.

If you burned 1 ton that would be the monthly power consumption of my house.........Rod.

Rod, there are different approaches for waste to energy. Here in Fairfax county, VA, they have an incinerator and I think they generate steam or something to produce some energy. But that's incineration and it's primarily to just reduce the volume to the landfill. And it does that by about 80%.

Our system is plasma gasification which would take that waste down to almost nothing and probably yield more energy. I'm learning more all the time. OK, to be specific, we use both a downdraft gasifier (more traditional) to process organic materials like plastics, paper and banana peels. Then we use a plasma gasifier to get what the DDG didn't get. We also accept metals in the waste stream and recover them as a mixed metal alloy. Non-organic elements are vitrified in molten glass and rendered harmless.

I think Roger gave me what I needed. x btu's per hour = y kw/hr.

[Peter Christensen]

If my math is correct and I'm not totally sure it is. 2000lb x 2504watts = 5,008,000watts divided by 1000 = 5,008 kilowatts divided by 24hr = 208.67 kilowatts per hour. My house used 619 kW.h in the month of September. I think you'll have a small surplus of power.

[Frank Pratt]

BTUs & Watts are not comparable. A BTU is a quantity of energy, while a Watt is a rate of energy use. You can compare BTUs to Watt/hours. I would be leery of any site that is trying to convert BTUs to Watts.

[andrew whicker]

If you had a way to store 1000 Watts (from whatever energy source and stored in whatever way) and you had something that required 5 Watts / hour, then you would get (1000 / 5 = 200) hours of use out of that stored energy.

[Alan Caro]

Roger Feeley,

There are a number of ways that waste products are converted to energy. When you mention "gasify" I think of converting wood products to "woodgas", which contains Nitrogen, Methane, Carbon Monoxide and various other gases. When this is properly processed, it can run an internal combustion engine. Think of it as a kind of low-level propane. It is not very high energy per unit volume and has to be stored compressed. It's a bit difficult to handle and to make efficient requires having to make large volumes to offset the cost of the generator, filtration, and storage devices.

In CA, communities create tiered landfills of organic waste, install a system of collectors and collect the considerable amount of Methane generated.

There are other facilities that burn waste to generate steam and this is done on a quite a large scale, but the difficulty there- which is a problem with woodgas in that there are quite a lot of greenhouse gases produced and other pollutants- carbon monoxide is not friendly. Methane is many times as powerful as Carbon Dioxide as a green house gas. Methane is such as serious pollution, that cows farting is major contributor to global warming.

My niece and family in Vermont looked into running a wood pellet boiler to replace the oil one to heat their large 1911 house, but the new heating equipment would have cost almost $30,000 and there's a lot more maintenance as the pellets burning leaves a residue. You have to look at alternative energy from all kinds of angles- pure electric cars cause pollution too by way of the electrical generation to charge the batteries. Hydrogen was going to be The Next Big Thing, but it takes a lot of energy to separate the H2 from the O.

In Los Angles, I used to sometimes see- and smell an early 80's Mercedes 230D driving around and it smelled exactly like a donut shop as it was running on recycled cooking oil. It was pale yellow-sort of a French fry color as well,..

Some interesting possibilities.

Alan Caro

[Steve Demuth]

BTU/lb of MSW = 8546 = 2504 watts

But I'm used to thinking of electricity in terms of a continuous flow. To me, that 2504 isn't the same as what I think of in an AC circuit.


There is some unit mixing in that statement that doesn't work. You can't compare watts to btus - they measure very different things, as you intuited.

Thiis is saying you could get 8500 btu by gasifying and "burning" a pound of waste. That 8500 btu is about 2500 watt*hour or 2.5 kwh. You can compare that easily to your electric bill. In all probability, you use between 400 to 1000 kwH each month. It could be more if you've got electric heat, but it'll be on your bill either way.

So, say your bill says last month you used 1000 kwh. Consider each "unit" of gasified energy to be 2.5kwH = 8500 but = 1 lb of waste. So, to satisfy that 1000 kwh of use, you'd need 1000/2.5 = 400 "units" of waste based power - or 400 lbs worth.

All that assumes you can turn gas-fired btus into electricity with 100% efficiency. You can't, of course. Even a big, modern super-efficient system only reaches about 65% thermal efficiency at high duty cycle. You won't get close to that with a high variably load. I'm guessing here, but I don't see how you'd get beyond 33% thermal efficiency with that kind of load in a small system. So you might need 1200 lbs of waste.

[Grant Wilkinson]

@Roger. Do a search on Plasco and you will find a lot of information on gasification. Plasco tried to get a plant running in my city - Ottawa ON, and they could never get the plant to process anything close to the theoretical performance. The local entrepreneur gave up on it and it's being dismantled.

[andrew whicker]

The more I look into gasification, the more I'm confused by the question.

1 lb of municipal waste is burned and has so many BTU's? 1 lb of municipal waste tuned into syngas is worth so many BTU's?

Are you looking into making a live project that takes in corn stalks or something? This looks like a complicated chemistry project.

[Jim Falsetti]

Roger, I know a little about gasification. Gasification, also known as partial combustion, typically uses feed like petroleum coke, coal, natural gas, residual oils, etc., and is a well-established commercial technology. The higher the energy content (BTU) the more good stuff is produced, and the less undesirable stuff is produced. After gasification, there are typically additional processes where nearly all the contaminants are removed and the resultant carbon monoxide and hydrogen mixture (known as synthesis gas or syngas) can be adjusted to the proper mole ratios for the desired end products. If you are gasifying very low BTU materials, such as low rank coal or MSW, the gasification efficiency is pretty poor, and yields are low.


The gasification process consists of the gasifier itself, and then all the stuff to separate solids from the gas, remove the contaminants, adjust the CO/H2 ratios, and purify the gas. Lots of equipment is required. The economies of scale generally preclude small plants with poor feeds. The contaminants in MSW are difficult to predict and then design for, the MSW feed stream is quite variable in quantity, composition and BTU content, and although plasma is often seen as a solution, it is a poor one. I believe every single plasma gasification process, and there have been several over the years, has in the end been technically unworkable and uneconomic.

In the USA, layer in super cheap natural gas, and a NIMBY (or NOPE) group, and you have a very difficult road ahead.

Apologies for such a long post, and hope it is some use to you.

Jim

[Kev Williams]

Sounds too much like fusion to me, where the net 'new' energy is less than the energy needed to create it...

[Stan Calow]

Andrew hit on the common problem with all energy production - no efficient way to store energy from when you can have peak production, to when you have peak demand.
Converting waste to energy is difficult partly because its not a continuous homogenous mixture of degradable stuff. Too much plastic, wood, metal and not enough carbon-based biomass. Like Kev says, it takes more energy to process it than you create.

Sorry for all the negatives - maybe you'll come up with a solution.

[andrew whicker]

One article I read mentioned that naturally decomposing dead stuff releases CO2 and CH4. Burning it releases only CO2. It's better, climate change wise, to burn it.

Gasification used to combat global warming seems to be net CO2 zero or at least adding less CO2 to the atmosphere for a given amount of energy than typical. Something about the feed stream needing to be 'bio mass' which I think is recently dead plant stuff, but not sure.


Anyway, none of it is going to be economical if we don't artificially raise the cost of energy. Washington state had a ballot initiative to add CO2 tax and failed. Big oil came in and scared residents. Claimed the economy would fall apart.

Dark times ahead when no US state even has a carbon tax after all the science we know.

In my opinion, if course.

I give money to offset my CO2 emissions when I travel via plane. I'd like to pay for my annual CO2 creation too after some simple calculations.

Lately I've been giving to a project that removes NOx from the exhaust of a fertilizer plant.

[Ole Anderson]

Capturing landfill generated methane is very common on large landfills. It is used to run large NG spark (not diesel) engines hooked to generators to generate electricity. Of course they don't last forever, the methane eventually runs out as the decomposition slows down. Drive by most any large active landfill and you will see a generating station.

[Bill Dufour]

The Nazi's even managed to run tanks on wood gas.

http://www.tanks-encyclopedia.com/ww2/nazi_germany/gas-powered-fahrschulwanne-tanks.php

https://en.wikipedia.org/wiki/Wood_gas

[Andrew DiLorenzo]

A watt is one joule per second. There is the time aspect needed for your analyses, short of going into full dimensional analyses.