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Story in this weekend’s Observer newspaper:
How melting plastic waste could heat homes.
The story is about a type of pyrolysis plant that takes the process further to produce hydrogen. The story doesn’t actually use the word pyrolysis, and by talking about clean hydrogen energy it taps into the current “hydrogen economy” rhetoric that is being used by some people.
The information appears to come from the University of Chester website. But there isn’t much extra there either. To me, it sounds like they may just be using a variant of the old coal syngas process – which requires steam and a carbon source to reduce water to H2 & CO. In this case they are using mixed plastics instead of coal, and may also get CH4, amongst other gases.
They are talking about collecting the H2, for sale, and burning the rest of the off-gases to make electricty. As such, this is basically an EFW (energy from waste) plant, that collects hydrogen as a byproduct. It looks like the combustion products (including CO2) will still enter the atmosphere – so, arguably, like all EFW plants it is just displacing an equal amount of fossil fuel use.
At least it will consume a lot of plastic – preventing it entering the oceans – even if it does pump out CO2.
I can see that any duckweed grown for food is going to need “clean” conditions, but the stuff grown for biofuels should also be good for wastewater remediation.
Many sewage treatment plants are currently building biodigester facilities to generate gas and make electricity. Another stage of water cleanup from duckweed might also help to provide extra feedstock for co-digestion – possibly enhancing the methane yield. The methane yield from pure sewage is not actually that good (although they process such a lot of crap that it is still worthwhile doing). Hence, at some plants they are also taking waste food to add to the digesters.
Unfortunately, some facilities seem to be using non-waste food, such as maize, for co-digestion – just because it is locally cheap.
If duckweed is to be used on a large scale, as a biofuel feedstock – then we do need to imagine what that would look like. One problem with current biofuel options is that people expect the crops to be grown “somewhere else” – so to not make any changes to their local scenery. But most of the good land situated “elsewhere” is already being used to grow food – and so biofuel crops simply displace food crops.
For biofuel crops, we need to use “marginal land” – such as hills and mountains. What would that look like? I’m guessing that for growing duckweed, terracing might just work – a bit like the way some rice paddy fields are arranged.
Try using the search function.
I guess this is one way of making a cold frame using bottles…
Have you read the reviews?
Maybe starting small, by making cloches, would be a good idea.
Having just had a healthy courgette plant demolished by the local wildlife – I think I’m going to have to do something to protect some of the more vulnerable plants in my garden, and cold frames or cloches are probably going to be the cheapest thing to build.
I’m guessing that wooden frames glazed with flattened panels cut from 2 litre PET bottles might just work. Alternatively, reclaimed clear polythene sheeting, or reclaimed glass (preferably toughened) could be used for glazing – with the side panels or framework made from re-moulded recycled HDPE.
Yeah, if the sun is entering the room, and hitting walls/furniture, then the overall heating benefit should be the same. You just won’t have a concentrated stream of warm air out of a can stack.
And yes, if PET doesn’t block UV, then I guess it might be possible to use such a bottle array to kill bacteria in tropical sunshine. I would think that you would need narrower bottles, though, so the UV can fully penetrate.
@donald – from a hot-surface-to-air heat transfer perspective, all that gluing of the cans is probably a waste of time, effort, and glue. If the whole glazed frame is sealed front and back, then you might as well scrunch all the cans, spray them black, and randomly fill up the framework with them.
That way, the surface area for heat transfer will be increased, as the air perculates (or is blown) up around the cans – and it will also create more turbulence. n.b. Surface to air heat exchangers are some of the most difficult to design well.
It looks like the plastic bottle ones are water filled – which might keep plastic surface temperatures down to manageable levels – if the flow is high enough. However, stopping all those bottle-to-bottle joints from leaking won’t be easy. And if the water temperature does get too hot, then the bottles will distort and shrink – which will definitely split the joints. 😉
And they have a verson 2 with some interesting joints made from plastic drainpipe. But, as discussed in other forum threads, drilling into the ends of the wooden beams is not a good idea – as bending loads are likely to split the wood.
Have a look at this thread. A number of the comments are about corrugated roofing sheets, mostly made from tetrapak waste (pulped, cardboard seperated, and the sheets moulded from the remaining polyethylene.)
I guess extra (low density) polyethylene could be also be added – such as waste plastic bags.
Hi @sarahg – after filling your survey questions, a little while ago, I’ve been pondering the geodesic dome greenhouse idea – so I might as well add some thoughts here.
I suspect a lot of people see geodesic domed structures and get a little buzz of enjoyment just from the way they look. I know I do – although I can’t exactly say why. Is it because of their geometric symmetry? Is it because most built structures tend to be rectangular cuboids – so the domes just look different? Is it the patterning of the framework that makes them look cool? I’ve no idea.
I’ve certainly always fancied the idea of having a geodesic dome greenhouse – and I’ve even looked into the possibility of building one – before various things put me off.
The first disadvatage I see is the circular ground plan. If you have the room for a circular structure, then fine – but in most small gardens, a rectangular greenhouse usually fits in better, without losing space. Even arched polytunnels have a rectangular ground plan – and so can be sited next to each other without creating any inaccessible external patches.
The other issue is the glazing. If using hard sheet material (e.g. agricultural glass, clear unplasticised PVC, polycarbonate) then cutting the triangular shapes could be quite wasteful. I guess there would be an optimum nesting scheme for cutting the different shapes of triangle from standard rectangular sheets – which would make certain sizes of dome more or less economical to build – and that would have to be carefully thought out at the design stage.
Sealing the glazing at the corners could get a bit tricky too – although for most greenhouses it wouldn’t matter too much if it was a little bit “leaky”, I guess.
The other method of glazing, by using flexible plastic sheeting is probably easier (and cheaper) – but that might also be a bit wasteful, compared to (say) covering a polytunnel.
But, yeah, geodesic domes are cool – which is why they turn up in all sorts of places. 😉
It was a bit of a disappointment, last night, when I saw that Fimo used PVC. I had always assumed it used some kind of thermosetting resin.
Looked at it many years ago, for home workshop rapid prototyping & ‘proof of concept’ purposes. But as you say @s2019 there might be more suitable materials.
There are filled epoxy “putties”, that start to cure after kneeding, and there are 2 pack polyester-based “fillers”, which might work too.
I guess people might have written about these before, in the forums.
How about using something like FIMO to create the mould? It should be malleable enough to form around your 3D printed “pattern” – and then you might be able to split it into two halves, using a sharp blade, and remove the pattern. The halves could then be fired (cooked) in an oven, whilst hopefully holding the detail of their shape. Fired Fimo is relatively strong, but you would have to see how it behaves during injection. My guess is that it would be better than silicone or plaster, as long as the heat of injection doesn’t soften it (which might happen).
PET bottle solar collectors?
Hi @timberstar – there are lots of cheap ways to build wet scrubbers. For the chemicals we are talking about here, PVC drainpipe & other fittings available in a typical DIY store would work fine. Upcycled PE drums – as you mentioned – would be fine too.
For random packing, the traditional method is to use Raschig Rings. These could be made by chopping up lengths of pipe. (Way back, when I worked in the nuclear industry, we used borosilcate glass Raschig rings in off-gas scrubbers – just as mentioned in the wikipedia article).
I suspect ‘Lye’ (sodium hydroxide) could work for at least some of the VOCs, as they might create a “soap reaction” (although that might not work at the low temperatures involved). I guess it depends on how reactive the volatile hydrocarbons are.
I’ve even read one article that reckoned that the newly created soap can help to emulsify more VOCs than are involved in the original reaction. Hence, you could possibly use a soap solution from the start (safer than the hydroxide), and just rely on forming an emulsion, rather than a solution.
@irismongolia – regarding the bran, I see that the composition includes some oil, which might help with VOC retention. Whether that would mean that rice bran would work better than wheat or rye bran, I don’t know.
@donald – the V4 washing project already includes sand bed filtration. So they will eventually need to do something with the contaminated sand. Anything that locks it up, along with the contaminants/microplastics, has to be better than landfill. I guess it could be mixed into conventional concrete – unless the microplastics just float to the surface… 😉
@irismongolia Great – I look forward to seeing the results 😉
I guess it would also be possible to partly pyrolyse the bran to make it more active, if it could be done without using a lot of non-renewable energy in the process (e.g. maybe by using a solar oven). But who knows, maybe raw wheat bran will be enough, if the air flow through the filter is handled sufficiently well.
Yeah, I was going to mention that one of the problems of desorption is having somewhere to send the nasty stuff once it comes back out of the filter 😉
The problem isn’t how to make a reusable cup. Coffee houses were using perfectly reusable cups in the 17th century. The cups were made of ceramic, and could be used hundreds (possibly thousands) of times.
Today’s coffee shops also have reusable ceramic mugs (usually stupidly large – which is another discussion). But the real problem today is the way that people feel that it is fashionable to walk around caryying a hot drink.
Of course coffee retailers love this – as it enables them to sell overpriced gloopy sweet frothy sewage to people who actually don’t like coffee (the people who do like coffee, drink it strong and black). Furthermore, the “latte/capucino to go” brigade don’t even take up any space in the shop – so it’s pure profit!
To facilitate this, retailers have used the disposable coffee cup – which taints the coffee with either a plasticy or carboardy taste. However, fashion is a powerful driver – and to walk down the street carrying takeaway coffee must have some kind of metropolitan caché, so taste, and the ability to calmly sit and enjoy a well brewed beverage, are irrelevant.
But people are now being gripped by single-use angst. They feel that it is no longer cool to be seen walking down the street with a disposable cup. They now want to carry a cup emblazoned with the words “biodegradeable” or “reusable” or “turtle friendly”.
The question is, will people actually reuse a “reusable” plastic cup? To reuse it, they will need to carry it home when covered in congealed milky froth, then wash it to a sufficient level of cleanliness that it doesn’t make the next refill taste even worse than normal, and then they have to remember to carry it with them every time they visit their favourte coffee vendor. And if vendors offer a discount to people using their own cup, then fashion concious people might feel that it makes them apear like they are short of money…
So should we be encouraging this lifestyle? Or should we be reviving, and updating, the 17th & 18th century coffee house?
For anyone faced with having to make an air extractor, instead of just buying one, this article (and video) is quite handy. Actually, I think it is interesting for its own sake (I’ve been in awe of this guy’s workshop experiments for a few years).
@donald I was going to mention acetic acid (vinegar) in the list, above, but could only find one reference (that was rather vague).
At least it isn’t as bad as the stuff I was having to mess about with 35 years ago – where the end result was inevitably a large tank of radioactive liquid 🙁
They can, indeed, be very simple (and cheap) to make – and can be very effective at particulate removal. I don’t know about VOC removal, though, as the scrubbing fluid has to be capable of absorbing the chemicals – and mustn’t create its own pollution by sending nasty vapours out of the chimney. 😉
Edit: Been looking for suitable (cheap and non-toxic) fluids that could take VOCs out of the air in a wet scrubber – and some suggestions are:
– Vegetable Oil (any oil of low volatility)
– A water / surfactant solution (e.g. soap or detergent)
– An aqueous caustic solution (e.g. sodium hydroxide)
Of course, you are then faced with having to dispose of a liquid contaminated by VOCs…
I’m sure @irismongolia will be able to correct any of this, and offer some sensible advce 😉
@marcvdv – that’s odd. the link still works for me. It goes to:
Most people in these forums are busy doing stuff. There is useful information here, on many topics, but you are going to have to do a bit of work to find it. Like all collaborative open-source projects, people are more willing to spend some of their valuable time answering specific requests if they get to know a bit more about the person asking, and if there seems to be a genuine prospect of some two-way information exchange.