Diary of an engineer: Capping the laughing gas

Submitted by AWL on 13 April, 2021 - 4:41 Author: Emma Rickman
Engineering plant

The apprentices haven’t seen each other since November, and it’s good to work with L. He has a lot of electrical knowledge, works diligently and has a very cool head. We work together installing a fan in the workshop (P’s fan, we call it, as it was his idea). Free of supervision, we can take our time cutting and tapping metal conduit so it fits snugly against the ceiling, running the cable neatly and listening to L’s “classic rock” playlist — now and then L breaks out in songs and head-banging. He’s twenty-one, likes cars, fishing, and scotch whisky.

We learn this week about two projects the plant managers are planning: clinical waste disposal and carbon capture. Clinical waste has been talked about for a while, but it’s finally been given the green light by the regional director. The Energy Recovery Facility’s (ERF’s) yard will become a sorting area for clinical waste from local hospitals; it will be separated into what we’re calling “low-medium” and “high” grade hazardous waste. We don’t know the details yet, but we think that “high grade” clinical waste includes used syringes, body parts and unused drugs; this will be burned at very high temperatures at a different site. “Low-medium” grades are bandages, nappies, tampons — anything contaminated with bodily fluids — and the huge quantity of PPE used for protection against covid. Our plant will be installing a railing for an automated skip-on-wheels that will tip the waste directly into the furnace.

The Carbon Capture project comes to us as an instruction from the Head Office in Paris. We’ll install some apparatus (as yet unknown) to remove carbon directly from the stack; this will mean installing machines and silos at the stack’s base. Sheffield will be one of the test sites for this technology, and I think it’s a win-win idea. The city council and my employer will be able to boast about carbon reductions — maybe even make a profit from selling the captured carbon — and there will be less pollution in the air for everyone. Alongside this, new emissions limits are coming into force — the plant has a new chemical analyser that measures and documents harmful gases we send into the air.

Before 2021, we measured Dust, Carbon, Hydrogen Chloride, Carbon Monoxide, Sulphur Dioxide and Oxides of Nitrogen.

Sulphur Dioxide (SO2) and Oxides of Nitrogen (NOx) are the big pollutants — we might burn something strange in the furnace and the SO2 trend would spike, setting off alarms and leading to frantic running around, slowing the burn and throwing in lime. This year, we’re being asked to cut SO2 and NOx even further, which is good. Both substances cause acid rain and NOx is harmful to humans as well as being a greenhouse gas. The ERF sits in a bowl between hills, next to a railway line and a major traffic intersection — Sheffield’s air quality is terrible, and we’re adding to the cocktail of problems.

However, this year we are also beginning to monitor and cap emissions of Nitrous Oxide. The electricians mull this over:

J: “N2O isn’t it? Two nitrogen one oxygen…?”

P: “I think it’s a motor propellant. You add it to your fuel for a bit of extra umph — we shouldn’t really be burning anything with petrol in it should we?”

After a quick google:

A: “Ah — it’s laughing gas! Ha!”

J: “Well we should start capturing that...”

Me (reading): “Good in medicine….dentistry...major greenhouse gas — yep, let’s get it!”

• Emma Rickman is an apprentice engineer at a Combined Heat and Power plant


Submitted by David Walsh (not verified) on Wed, 14/04/2021 - 11:03

As someone who was involved in one of the 'first generation' of EFW plants which replaced a dirty 60's incinerator complex, a tip on clinical waste. One idea kicked round, but not adopted as in the end there was no clinical waste stream added, was for the “low-medium” grades of the time (now a far larger stream given the expotential growth of wet wipes and now PPE) to be hoppered into the furnace chamber by taking it through a sealed room at lower bar air pressure.  This would have avoided 'blow back' from the hot air from below pushing back on to the disposal gallery area with the risk of conentrating airborne pollution and bacteria.

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