Steam Loco exhaust, ex-34081 - 92 Squadron

One problem with biomass is the energy density and physical density. In rough numbers the calorific value is around half that of coal, and the density similarly about half. Thus the volume of fuel required is about 4 times that of coal. I'm not sure what the ash volumes would be. It also seems that variability is also an issue, systems seem to need to be designed to suit the fuel be it woodchips, miscanthus or whatever.

Rob

 

Perhaps putting coal dust in it would increase density as well as making it smell right...

 

Didn't the French make a lot of use of briquettes, and didn't those consist essentially of coal dust glued together?

 

Didn't we have 'ovoids' here for a time ? esp post war ...look promising but would be sludge after being rattled about in a tender for a while ?

 

Although not a true gas producer Sentinels have water filled ashpans, which will fizz and bubble away, and can have a noticeably negative effect when dry, particularly on harder coal. Watching Sentinels after dark can be fascinating with effects ranging from 'Bunsen Burner' flames from the chimney to spark arresters glowing like gas mantels. I once talked to a couple of blokes who took particular interest in the water filled ashpan before getting all scientific about it with the types of formulae shown earlier, and deciding that there was more to it than just not dropping burning ash onto the road.

 

Mercifully, torrifid biofuel pellets (I'm abbreviating this to tfp from here) don't necessitate the complex driers of the Bulleid turf burning system. The current production techniques indicate it wouldn't be correct to think about tfp in terms of peat or less highly processed plant products. Regarding density, you'd have to expect that of tfp to be way lower than coal, pressures and times taken to produce the latter being massively greater. As to range of calorific values, tfp is claimed to be some 22% lower than the upper figure of the range quoted for coal, while moisture content is listed as 10% that of coal. I don't have the expertise to speculate on how this impacts on design changes needed to get the best from this fuel.

The attached page from the Coalition for Sustainable Rail provides direct comparisons between wood pellets, charcol, torrified biomass and coal:

http://csrail.org/torrefied-biomass/

Coal briquettes (mentioned in earlier posts) were once common in Ireland. Plenty of later photos of the T&D clearly show these stacked on just about every available horizontal surface on the amzingly rugged (and pretty much worn out) Hunslet 2-6-0t locos. The C& L also seem to have used them, despite the main reason for the line's survival being coal traffic from the mines north of Arigna! I believe these briquettes were an attempt to eke out the indifferent coal supplies during and after WWII. Being more uniformally aerodynamic than random lumps of coal, they seem to have found favour with loco firemen for discouraging sheep from the three foot!

(I've just noticed a near identical url, csrail.org.uk for the Central Suffolk Railway... a seperate thread for any discussions of that one, please!)

 

These effects would indicate that there is insufficient secondary air above the fire to burn off the gases. A lot of wasted heat that could be going into the boiler.

 

i remember those coal ovoids, coal dust held together with PVA i think they were,
we didn,t call them ovoids though, and i would get admonished and deleted if i said what we did call them,

and the way forward is,

PROPANE,

 

We used similar brickettes on summer made mostly out of Lady Windsor coal. I preferred them to the straight coal.

 

Methane.

 

Must be the onions...

 

on a serious note, as much of the coal mined now is open cast, with i assume a lot of unusable coal in the form of dust, or sub standard, can anything be gained from forming some coals into brickets if a uniform product with known calorific value would be made would it be suitable for use in steam engine fireboxes?

 

Yes I remember them, shall we just say the were named after males . The East Midland freight sheds mixed the "ovoids "with Leicestershire mined coal, from Whitwick mostly, that coal had plenty of ash content to say the least.
The East German converted 25 class 52s ,and classed them 52.90, to burn pulverised brown coal. They were converted in 1970 but all withdrawn between 1975 and 1980. The were allocated to Senftenberg depot .I was phographing, in 1976 ,on the Dresden to Berlin main line several miles south of Elsterwerda, near to where the cross country line from Senrtenberg to Falkenberg crossed ,that is one of the lines where they worked .Had I known at the time I would have made the effort to go the few extra miles to see if I could have seen one of these rare machines . However news on freight train at that time in the GDR wasn't easy to get.One is preserved in Dresden ,or it was a number of years ago.

 

It's worth remembering that Sentinels mostly have vertical boilers (I'm guessing it's this variety the original post was about). So there's no brick arch to improve gas phase combustion and thus volatiles have an extremely short time to burn in the firebox before passing through the water-tube section and out into the chimney. They're also chute-fed from the top, which probably doesn't lend itself to a good secondary air supply and would be in danger of just cooling the boiler if excessive. The effects @clinker described are actually quite reminiscent of Holcroft's description of coke-burning locomotives in the 19th century (Locomotive Adventure vol 2):

"So for the next 30 years locomotives burnt coke in their fireboxes, and this needed a deep fuel bed. When steam was shut off on a run gas-producer conditions resulted and at night the lambent flames of carbon monoxide issuing from the chimney were visible."

These boilers would not have had a brick arch, so again would have tended towards incomplete combustion of gases in the firebox. What strikes me about the description is the flames from the chimney, I was wondering about the re-ignition even after the gases had passed through the tubes. (609 deg C autoignition temperature for CO) but I guess hot unburnt fuel particles could also act as an ignition source once in the oxygen of the atmosphere.

 

the potential for a gas producer fire to be 'put out' , and then re ignite with some force, has been noted.

 

Yes, The Sentinels that I referred to are vertical boilered, in fact road waggons, the height from the grate to the chimney base is in the region of 4' and they are top fired, through a chute that ends about 1' above the grate, some operators have drilled a hole in the firing lid, which has a baffle plate below it, some leaving it open, some having a 'flap' to close it off. As 8126 pointed out, there's no brick arch, but some have fitted a half baffle below the superheater coil, in line with the chimney base to deflect some 'fire' back onto the rear of the superheater coil, which does improve matters, this was first fitted by the foreman in Sentinels Liverpool depot, and carries his name, The Jimmy Stotts Plate, some waggons have been fitted with a double coil superheater in the belief that the steam will be hotter, but in reality it will just give a better 'supply' of steam at the same temperature, or maybe slightly lower, a JSP is almost certainly required. The flame out of the chimney will happen with the regulator open, and when really going some you daren't lift the lid unless the regulator or blower is open.

 

https://i.imgur.com/BzdSJsm.gifv

China apparently - and provoked by slipping...