Low energy smoke abatement system

roasting & roastery operations

Low energy smoke abatement system

Postby paul_pratt on Mon Aug 04, 2008 9:52 pm

I thought I would contribute a little info on this system which I have been running now for around a year and a half. It may be useful for people with small roasters like mine who are in built up areas and it is also appropriate at this time due to the fact that it uses very little power. Although roasting is not a huge part of my business anymore I still like to have the ability to roast for fun whenever I want and of course I need coffee for our own consumption.

Hong Kong does not have any single storey factory buildings, therefore dealing with the smoke is a big problem. You have 2 choices, either find the top floor of a high-rise factory bldg., or install a chimney up the side of the bldg. The latter option is just not economically viable and it has proved difficult to find a suitable top floor premise. The other main problem is gas supply, these factory buildings just aren't equipped with mains gas installations so running an afterburner is tricky. You can of course have mains gas installed but again not economicaly viable.

My solution has been to use my own custom built smoke system. This allows me to roast during the daytime and vent the exhaust air out the window without any problems from the neighbours. A few years back I discussed with a ventilation company who make smoke hoods for kitchens, we got talking and tried to get our head around a solution for a small coffee roaster. The idea we came up with is we would incorporate one of his smoke hood "cells" with a water scrubber and ventilation system. The other important functional element of this system was that it needed to be portable and required little in the way of dismantling should I move office or relocate back to the UK full time.

So here is the roaster, a little LE5 (4.5kg batches) which I adpated with a profiling system from Eurotherm. We can upload profiles, plot and datalog on the laptop if we want or run it in full manual mode. Yes, the roaster in the 1st pic is perched on some blocks :D so that we can wheel a pallet trolley under it and move it around for cleaning.

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Above the roaster is a smoke hood that sucks up smoke from the beans when they drop into the cooling bin. That is a bit excessive and unecessary but it means no smoke inside the room. The smoke hood works because it has negative air pressure caused by a powerful fan unit at the smoke scrubber system. We also have our spotlights mounted onto the smoke hood.

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So the output from the roaster meets with the smoke hood pipe and then travels around 5 metres through my playroom where it gets to the scrubber.

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The scrubber unit is tucked away in the corner out of sight. It is around 2 metres high, 60cm deep and 1m wide. I will explain more of the scrubber in detail later. In this final picture, you can see the input pipe (from roaster) at the top of the picture and it drops down into the scrubber. 2 collection cells are seen infront of the unit on the floor. The clean output to the outside is via the blower unit on the top.

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Re: Low energy smoke abatement system

Postby paul_pratt on Mon Aug 04, 2008 11:08 pm

How does it work?

1. Smoke leaves roaster and goes through the double-walled pipes to the scrubber.
2. Passes through an emergency chaff collector - it does catch a fair amount.
3. Enters into a water spray chamber which cools it down, labelled A
4. Goes through a pre-filter screen
5. Goes through the ESP cell labelled B
6. Then exits the system and out the window through a powerful blower.

Here is an older picture of it taken when we were testing it. What you can't see in the picture is the blower unit. Basically the smoke goes from A to B.

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All of the work is really done at the last stage, in the collection cell - the ESP which stands for Electrostatic Precipitator. The idea is that the smaller particles like odour and the oil from the coffee pass through an ionizor and are immediatly charged. They then pass through an oppositely charged collection sell to which they are attracted, leaving the oil desposited onto the plates of the cell. Basically like a big magnet for coffee oils. This part of the system is the bit that is usually a component of kitchen venilation systems to remove cooking oil smoke.

The main control panel with the on/off switch and alarms.

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The door to collection cell that contains the electronic components that power the ESP collection cell has to be locked with a key to prevent accidents. Inside there are 11kw high voltage transformers.

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Below are 2 of these collection cells, yhey weight about 5kg each. The coffee oil is left on the plates of the cells in the form of a thick gooey film. The cell slots in and out of the unit and you can change a cell within a minute if need be.


Using it for roasting

The unit is switched on the whole time you are roasting. Before I mentioned we have a powerful blower in this system. The blower is positioned after our scrubber system and it has 2 functions. The first is to draw the exhaust smoke from the roaster and the smoke hood and pull it through the water spray and collection cell. The second function is to expel the cleaned air out of the window.

I said that I have been using it for 1.5 years now and it is amazing. We had around a 3-4 month teething period where we worked on the system and made adjustments. The biggest issue has been balancing the blower power with smoke reduction efficiency, i.e. there is a critical rate at which you pull air through the system and the system can work properly. The other issue that I thought would be a problem was that too powerful a blower would somehow effect roasting times but it was never an issue as we compared control roasts (no blower) and with the system on full power and roast times and temps were the same.

It is possible to notice a little visible smoke going out the window if doing a french roast but that is it. People who come to visit are amazed at how well it works. Whilst the odour of roasting has not been eliminated 100% the smell is a sweet pleasant smell rather than a burnt smoky smell.

We find that if we are roasting for friends or the few people we supply we can do around 8 hours on each cell which is approx 80-90kgs. After that the cell plates will become covered in oil and then they are required to be cleaned in an organic cleaner and then discharged down an approved government grease trap. When it is time to change the cell the machine has an inbuilt alarm telling us to do so.

We tested this unit and it would also work on a 15kg roaster. To be safe if it were me I would have 2 ESP units as opposed to mine which has 1.

Low running costs

The water cooling section of the unit uses water that is recycled and needs to be replenished every hour. But the best for last. This unit uses only 40W of electricity. If you add a pump like we did to recycle water you need another 300W. So all in all a smoke elimination system that uses under 400W power.
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Re: Low energy smoke abatement system

Postby phaelon56 on Tue Aug 05, 2008 6:49 am

Paul - that's just brilliant - thanks for sharing. I think there are many of us in the roasting community based in areas where afterburners are not required by code but who are open to smoke abatement options. The dilemma has long been both the high purchase cost of afterburners and their large fuel consumption. Your solution appears to address both issues.

Ballpark guess of cost in US dollars if one were to assemble such a system with a mix of prebuilt and customer built components? $5K... $10K... $15K... +++ ?
Owen O'Neill
Syracuse NY

Phaelon Coffee
and
New York Central Coffee Roasters
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Re: Low energy smoke abatement system

Postby paul_pratt on Tue Aug 05, 2008 3:11 pm

Hi Owen,

I am in the same situation as it was more for my peace of mind rather than regulation. I was fed up of having crappy industrial buildings and wanted something that would be ok to use anywhere. Now it is set-up in a nice building and so far no complaints, but we only use it once a week during the daytime.

All in all it was probably $5k incl. the main ESP unit, pumps, blowers, steel frame etc...not bad considering running costs are minimal.

Paul
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