Diary of an engineer: Hot Ash

I’ve been following the operations assistants around the plant to get an understanding of their duties. The messiest and most routine job on the plant is dealing with what’s left over after the waste is burned.

During shut-downs I’ve stood on the grate and tried not to slip on the slanting metal bars. It’s a steep incline of steps nicknamed “piano keys” which push up and down, rolling the waste “downhill” as it burns. Above my head is a huge space covered in racks of narrow metal tubes that curl back on themselves and hang down from the distant roof like chandeliers from a cathedral ceiling. These suspended assemblies of tubes are called “pendants”.

It surprised me that the gas burners which ignite the waste are a long way from the waste itself. The furnace is like an oven, but so hot that anything on it spontaneously combusts. Once lit, the burners switch off and the waste ignites itself in a continuous stream.

Of course, not everything is incinerated. At the bottom of the grate staircase is a pit called the ash discharger. Metal items, ash and rubble fall into this space, steaming hot and black. Ash and debris all fall between the ‘piano keys’ as they push the waste downhill. This ash is collected in “riddling” chutes and moved by hydraulic levers down towards the dischargers.

Clearing out the riddlings is a twice-daily job for the assistants. ‘M’ takes me to the space under the grate where these levers operate. It’s hot, dark, and there are the noises of invisible hot objects falling into the chutes.

“Never look into these chutes directly, or you could get a face-full of ash” says M, pushing a long metal scraper into the chute. “But you’ll often find cash in there – coins don’t burn and they fall through the grate bars.”

At the other end, the hot ash is plunged into a tunnel of continuously recirculated water. This creates an air seal between the furnace and the outside world.

“The dischargers are always getting blocked”, S tells me, standing ankle-deep in ash scraped from the tunnel. “Sometimes the ash is light, and just sits on top of the water. Then we get a build-up in the furnace, and we have to clear it out by hand.”

At our feet are pieces of bulky metal that the discharger couldn’t cope with: motor chassis, weight-lifting dumbbells, misshapen shopping trolleys. This kind of thing shouldn’t end up in a black bin, but it often does.

Once the ash is through the dischargers it’s hauled up by another hydraulic lever onto conveyor belts; soaking wet, heavy and still hot enough to steam. The welders show me a hole in the conveyor where this ash has battered and burned through the belt – they use every shut-down to weld fresh steel plates over it.

M’s job – rotated between three others – is to sweep and hose the ash conveyors each morning. The rollers beneath the belts clog up with wet ash, or are wrapped around with long pieces of scrap wire. He uses a power hose to wash ash into a collection bay. I take the hose from him for a while and the force of it pushes me back against a wall – I fall towards a railing when I let go of the trigger and crack up laughing.

“And now we squeegee the floor.” M smiles “It’s kinda satisfying. There’s a feeling of pride in your work, when you’ve made it safe and clean, and everything functions.”

Despite the power and complexity of the machines that make up the furnace, the system would fail without constant human attention.

• Emma Rickman is an apprentice at a Combined Heat and Power plant in Sheffield.

• Other entries in the “My Life At Work” series, and other workers' diaries