Waste-to-Energy Plant

Earthlink NTU is fortunate to be given an opportunity to visit the Senoko WTE Plant, made possible through the National Environmental Agency (NEA). We are thankful to be hosted by a friendly and informative installation officer, Max Heng at Senoko WTE Plant. Max shared with us about the processes that lie behind the incineration of waste, which will be in the article content.

The first stop of Earthlink’s Recycling Portfolio Waste Trail Journey: Senoko Waste-to-Energy Incineration plant.

What is your impression of a rubbish incineration plant? Black smoke in the air, foul smell stinking up the air or suffocating pollution? Surprisingly not! Take a journey with us into the Senoko Waste-to-Energy (WTE) Plant.

Senoko WTE plant sits tucked away in the northern tip of Singapore, right above Woodlands. Apart from the festive looking, 150m-tall twin chimneys, it looks quite ordinary. To the lay person, no one would suspect this to be one of the four centers for Singapore’s rubbish. Its identity is betrayed only by the frequent arrivals of refuse disposal trucks, and the ever-so-slight odor of rubbish.

Senoko and Singapore’s waste management

Senoko WTE is also the only waste incineration facility located outside of the Tuas area (west of Singapore). It is positioned to serve the eastern, northern and central areas of the country – no small burden for the plant. It receives 500-600 refuse trucks and incinerates close to 25% of the 10000 tons of rubbish Singapore produces a day.

The incineration operates 24 hours a day, 365 days a year. It simply cannot afford a day off. In fact, all 4 incineration plants in Singapore currently operate at high capacity to manage the refuse generated daily. This load will be shared by the upcoming waste-to-energy plant built by a Hyflux and Mitsubishi consortium, expected to be complete by 2019.

Do we burn… everything?

Because of Singapore’s land scarcity, most of our rubbish is incinerated. But not all rubbish is incinerable. Bulky objects will choke the hoppers (passageways for trash to be thrown into the furnace). They have to be broken down into smaller pieces before being sent to the plant. As such, they have to be collected separate from normal rubbish. Other non-incinerable objects like hazardous wastes or flammables are handled by special facilities suited to dispose of such wastes.

As a form of deterrence, 30 to 50 refuse trucks that enter SWTE are randomly stopped and painstakingly inspected for non-incinerables everyday. The selected trucks unload their trash onto the ground, and workers are deployed to inspect the trash before transferring the trash into the refuse bunker. Trucks with incinerables in them are sent back to the public waste collectors, for them to dispose of appropriately.

The incineration process: how it works

With non-incinerables aside, let’s get down to the real work the SWTE does.

Refuse trucks unload its trash into the refuse bunker, a 5-storey deep refuse storage. The bunker’s air is kept below atmospheric pressure, preventing refuse odors from escaping into the environment. A grab crane (or ‘the claw’) in the bunker then transferred the rubbish into the incinerator, lifting up to 5 tons of load per grab.

In the incinerator, the refuse is dropped onto a slanted platform known as the incineration grates which spreads out the refuse and evenly mix it with air, leading to complete combustion of the trash. The incinerator operates at an optimal temperature of 1000 degree Celsius, which is deemed as the temperature that will produce the least gas pollutants. The waste would end up as ashes, and will then be drop into a storage below the incinerator.

Flue gas (gaseous, often toxic, by-products) of the incineration process will go through an advanced flue gas cleaning system to remove dust and neutralize pollutants from the flue gas before it is released into the atmosphere via tall chimneys. Flue gases emitted are monitored real time and ensure that they meet emission standards set by the National Environment Agency.

The process reduces the volume of our rubbish by 90%, then the ash transferred to our only landfill, off-shore Semakau, to be stored.

Creating Green Energy

But Senoko WTE Plant not only reduces the amount of space our trash occupies, it contributes to green energy as well! The plant converts waste to energy, just as its name suggests. The heat that is released is channeled to the boiler to produce superheated steam. The steam is used to drive turbo-generators to produce electricity.

Senoko WTE Plant is fully self-sustainable, and has no need to burn fuel for electricity. This is because the refuse combusts spontaneously once the temperatures are high enough. It consumes only one fifth of the energy it produces; the rest is fed to the national grid. The surplus energy from SWTE is enough to power 100 000 3-room HDB flats per day! Together with the other 3 waste-to-energy plants, the total surplus energy generated meet between 2 to 3 percent of Singapore’s energy needs. Unlike fossil fuel power stations, WTE plants are unable to control the amount of energy generated; it varies with the type and amount of refuse that is thrown every day.

Going through the trash

While it certainly isn’t a glamourous job, working in Senoko WTE Plant does have its perks. Peer into the refuse bunker, and you can tell a lot about buying habits of the season. Our guide, Max tells us that it’s an amusing sight to spot amidst the rubbish hills durian shells in the middle of the year, Santa and reindeer decors at the end of the year, then huge dragon heads and Chinese New Year decors shortly after.

Senoko WTE doesn’t only burn dirty municipal and industrial waste. One does get a glimpse into the side of fashion industry few are conscious of. New, out of season luxury products are sent to the plant to be destroyed as company representatives look on. This ensures that out-of-season goods are not found at discounted prices which will undercut their business.
There’s more to WTE plants that we know! The trip the Senoko WTE certainly surprised us. Join us for Recycling Committee’s upcoming trips for our Waste Trail Journey and look forward to an insightful and informative time!

Curious about the SWTE? Here are some Frequently Asked Questions!

Q:
Are there days when there is too much rubbish for the plant to incinerate? What happens then?
A:
The rubbish is kept in the refuse bunker for at most few days before its incinerated.

Q:
How do we know how much trash Singapore produces?
A:
Refuse trucks that enter the facility are weighed on a weighbridge before and after they discharge their loads into large refuse bunkers. This weighing process enables the WTE to keep track of the amount of waste disposed of by each vehicle.

Q:
Why is it not smelly in the plant?
A:
The pressure within the refuse bunker is kept below atmospheric pressure, such that the unpleasant smell won’t be able to escape the bunker (air flows from high pressure to low pressure)

Q:
Are the recyclables present among the trash sorted and recycled?
A:
Any recyclables that are thrown into the general waste bin will be transported to similar waste-to-energy plants, where they will be burned to ashes. These precious resources could have been recovered in the Material Recovery Facility and made into new items. So please segregate your rubbish and give your recyclables a second life!

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Written by:
Gan En Xin Gladys
Ng Shi Hoe