OT: about coal gas and hydrogen

[The Natural Philosopher]

Really this is a separate thread response to Tim S who claimed that gas was made by pyrolizing coal to make coke. Yes, originally it was, and that gas contained not only carbon monoxide, but any volatile gaseous breakdowns of bituminous coal like methane. It was good for lighting because the sooty breakdowns of the carbon based compounds gave a yellow flame. That is 'coal gas'. A by product of coking. It contained no native hydrogen...

As far as I can tell Wiki says this

The first process used was the carbonization and partial pyrolysis of coal. The off gases liberated in the high-temperature carbonization (coking) of coal in coke ovens were collected, scrubbed and used as fuel. Depending on the goal of the plant, the desired product was either a high quality coke for metallurgical use, with the gas being a side product, or the production of a high quality gas, with coke being the side product. Coke plants are typically associated with metallurgical facilities such as smelters or blast furnaces, while gas works typically served urban areas.

A facility used to manufacture coal gas, carburetted water gas (CWG), and oil gas is today generally referred to as a manufactured gas plant (MGP).

In the early years of MGP operations, the goal of a utility gas works was to produce the greatest amount of illuminating gas. The illuminating power of a gas was related to amount of soot-forming hydrocarbons ("illuminants") dissolved in it. These hydrocarbons gave the gas flame its characteristic bright yellow color. Gas works would typically use oily bituminous coals as feedstock. These coals would give off large amounts of volatile hydrocarbons into the coal gas, but would leave behind a crumbly, low-quality coke not suitable for metallurgical processes. Coal or coke oven gas typically had a calorific value between

10 and 20 megajoules per cubic metre (270 and 540 Btu/cu ft); with values around 20 MJ/m3 (540 Btu/cu ft) being typical.

The advent of electric lighting forced utilities to search for other markets for manufactured gas. MGPs that once produced gas almost exclusively for lighting shifted their efforts towards supplying gas primarily for heating and cooking, and even refrigeration and cooling."

--------------------------------------------------------------------- So that was 'coal gas' Coke and hydrocarbon gasses came out of heated bituminous coal. No Carbon monoxide, no hydrogen.

Then came water gas and producer gas - or 'town gas'

-------------------------------------------------------------------- "Fuel gas for industrial use was made using producer gas technology. Producer gas is made by blowing air through an incandescent fuel bed (commonly coke or coal) in a gas producer. The reaction of fuel with insufficient air for total combustion produces carbon monoxide (CO); this reaction is exothermic and self-sustaining. It was discovered that adding steam to the input air of a gas producer would increase the calorific value of the fuel gas by enriching it with CO and hydrogen (H2) produced by water gas reactions. Producer gas has a very low calorific value of 3.7 to 5.6 MJ/m3 (99 to 150 Btu/cu ft); because the calorific gases CO/H2 are diluted with much inert nitrogen (from air) and carbon dioxide (CO2) (from combustion)

2C (s) + O2 ? 2 CO (exothermic producer gas reaction) C (s) + H2O (g) ? CO + H2 (endothermic water gas reaction) C + 2 H2O ? CO2 + 2 H2 (endothermic) CO + H2O ? CO2 + H2 (exothermic water gas shift reaction)

The problem of nitrogen dilution was overcome by the blue water gas (BWG) process, developed in the 1850s by Sir William Siemens. The incandescent fuel bed would be alternately blasted with air followed by steam. The air reactions during the blow cycle are exothermic, heating up the bed, while the steam reactions during the make cycle, are endothermic and cool down the bed. The products from the air cycle contain non-calorific nitrogen and are exhausted out the stack while the products of the steam cycle are kept as blue water gas. This gas is composed almost entirely of CO and H2, and burns with a pale blue flame similar to natural gas. BWG has a calorific value of 11 MJ/m3 (300 BTU/cu ft). "

------------------------------------------------------------------------ So that was the start of 'town gas' which killed you from CO poisoning, and was lighter than air and went bang. And needed a gas MANTLE to produce light.

Produced by partial *burning* of the coal and steam to create the hydrogen. I am not saying that some 'coal gas' was not in the pipes as well, but that the main way in which 'town gas' was produced was not by pyrolysis, but by *burning* in a steam laden atmosphere. i.e. 'water gas'

[Andy Burns]

Dad was a fitter at the local gas works before natural gas, he always talked about the coking plant, I'll ask if they added steam ...

[Sn!pe]

They taught us about "water gas" and "producer gas" at school, back in the dark (gas-lit) ages.

[The Natural Philosopher]

Not if they were making COKE. That is te point - gas - coal gas started out as a by product of coking, but in the end the demand for gas exceeded the demand for coke, so they switched to producer and then water gas to basically burn the coal and turn it all into carbon monoxide and hydrogen. No coke left!

[The Natural Philosopher]

Yes, as well as coal gas and town gas, and it is important to note that what was in the gasometers was not (much) *coal* gas, it was *water* gas

- aka 'town gas'. Producer gas was more an industrial gas I think.

The key differences are that coal gas is the hydrocarbon products of non oxygen heating of bituminous coal, whereas the others are all partial oxides of carbon itself plus the reduction of water by carbon to release native hydrogen.

With 'coal' gas you end up with coke and *hydrocarbon* gas. With the others you end up with a bit of slag, carbon monoxide, and hydrogen and that's it. No coke left.

[AJH]

I think they have missed a bit out, the products of the air cycle are CO and nitrogen and their production has heated up the coke and brickwork in the kiln to 1100C, the superheated steam is then reduced by the coke to H2 and CO but as the temperature falls due to the endothermy the swing occurs again at ~850C. The energy in the CO and nitrogen part of this swing process is not wasted as it is used to raise and superheat the steam. The 10% nitrogen is the residual nitrogen left in the kiln at the changeover.

Any of us who played with bunsen burners would have realised that town gas still was carburetted in that if the air valve was closed it gave a yellow flame, the yellow being glowing carbon particles in the diffuse flame where the hydrogen had been stripped from the hydrocarbon preferentially in the initial lack of oxygen diffusing into the flame. When one opened the air valve the ejection of gas into the air stream caused premixing by the time the flame held on the outlet hence the bright blue cone as there was adequate air in close contact with the fuel molecules which burned out the constituents simultaneously to CO2 and H2O.

I think the cold gas efficiency was in the order of 80% of the energy of the coal input ended up in the town gas.

In some ways the transport of coal to town gas works then the coke back to steel works drove the expansion of rail.

[newshound]

Ditto to Snipe.

That's a very useful summary of the history. I knew about the technologies, not the detail about "town gas". I still remember the local gas-works in the town where I was brought up (Epsom). My local railway station still had gaslight (with mantles!) into the 60's.

[newshound]

And canals. Didn't the Bridgewater canal reduce the price of coal in Manchester by a factor of 5?

[AJH]

I can believe that but don't know.

In Woking the gas works and the electric company were both next to the canal. I think the electric turbine was only there as the canal was the closest source of cooling water but presumably coal came to both of them that way.

Many commuters will remember traveling through Woking en route for Waterloo and seeing a chimney advertising Parazone. This chimney was near both gaswoorks, where production of gas stopped pre war, and the electric company, which I believe stopped generating in 1948, but I don't know what it was for.

The gasometers remained in use right up to natural gas around 1967 and beyond IIRC but none of the rest of the site was redeveloped till much later because or decontamination problems.

[AJH]

The farm where I learned to milk cows in 1973 only had electricity in the farm yard and a wire was strung from that to the farmhouse kitchen light bulb only.

The rest of the house was gas lit with mantles in open topped glass globes. I don't know if they worked post 1967 on natural gas.

The old [1] Scottish gent who was the tenant farmer still had a cardboard crate of the globes he had acquired during the war, just in case.

I pinched one when he sold up to make a macramé hanging basket and still have it.

[1] he seemed so decrepit and old but he was only 1 year older than I am now, forced to carry on farming because he couldn't afford the dilapidations as the farm became so run down.

[George Miles]

[newshound]

Acetylene generators? Like ancient car, motorcycle, and train lights?

[Tim Lamb]

Oil lamps?

>

[Chris Hogg]

Cow farts?

[Tim Streater]

Drip water onto calcium carbide.

[AJH]

The farm I was talking about was not at all remote, it was at the end of a residential street at the edge of the village.

The tenant farmer had simply not installed electricity to the house and the landowner had no incentive to do it.

[George Miles]

This old house had gas lights but no connection to a gas main.

So did they heat up coal > > > How did remote farms and houses make the gas for lights?

[Chris Hogg]

Bottled propane (LPG) has been around since before WW2.

[tony sayer]

Thats one reason they converted Cambridge to natural gas as soon as they could, as there were too many students putting their heads in gas ovens the natural gas wasn't as poisonous...

[The Natural Philosopher]

Yeah. Frankly they might as well not have bothered