The right technology for the right waste problem

Waste to energy projects often start with the wrong question.

Someone sees an anaerobic digester, a gasifier, a pyrolysis plant or another piece of impressive technology and asks “Can we get one of those?”

Technology is tangible. It gives a project something to point at, price and potentially fund. It even positions you for a grant or the latest exciting PR opportunity.

The better question is much less photogenic “What exactly is the problem we are trying to solve?”

The technology is rarely the right starting point

Waste streams are not interchangeable. Food waste behaves differently from timber. Timber behaves differently from sewage sludge. Agricultural residues behave differently from mixed municipal waste.

Beyond that, a whole range of parameters impact what the most suitable technology is:

• Moisture content

• Contamination

• Volume

• Consistency

Projects are often designed around an assumed feedstock supply that later proves too variable, too contaminated, too expensive to transport or simply unavailable in the quantities required.

The location where the waste is generated makes a big difference too – are there energy demands on site, for gas, electricity, heat etc? Do you have an outlet for the material you create?

A billion dollar lesson in choosing technology first

One of the more striking examples comes from Air Products in the United Kingdom, back in 2016.

The company developed a large energy from waste plant in Tees Valley using advanced plasma gasification technology.

On paper, the concept was compelling. Municipal waste would be converted into syngas and then used to generate renewable electricity, with much more energy yield than conventional waste to energy.

In practice, commissioning the first unit proved extremely difficult.

In 2016 Air Products abandoned the project after concluding that significantly more time and resources would be needed to make it operational. The company recorded losses of about US$946 million from exiting the business.

The lesson is that moving from a controlled technology concept to a commercial facility handling real, variable waste is a very different proposition.

During commissioning, a large number of design changes were identified that were required to operate successfully, including the burner and waste input angles, air flow control and other items. These could not be simply rectified. Gasification is used successfully on simpler feedstocks however it has not been demonstrated to be suitable for municipal solid waste.

A great example of how to beat this trap is the East Rockingham project in Perth, which was initially designed as a gasifier plant. It was converted to a traditional mass burn EfW process prior to final investment decision, due to cost and risk factors. This shows that they did not put technology at the head of the project, rather they were willing to switch when it became necessary.

Compare that with ReWaste

Yarra Valley Water’s food waste to energy facilities at Wollert and Lilydale are a very different example.

Here, the problem and the technology line up.

The ReWaste facilities receive commercial food waste from sources including food manufacturers, restaurants, markets, breweries and dairies, material that is well suited to anaerobic digestion.

The facilities also sit beside Yarra Valley Water’s sewage treatment plants, creating an immediate use for the energy produced. The energy powers the waste to energy facility and adjacent sewage treatment plants, with excess electricity exported to the grid.

It also aligns with Yarra Valley Water’s strategic objective to be 100% renewable energy powered and carbon neutral by 2030.

Anaerobic digestion, pyrolysis, gasification or combustion?

There is no universally best waste to energy technology.

Anaerobic digestion can be extremely effective for wet organic materials such as food processing waste, manure, fats, oils and other biodegradable streams.

Pyrolysis may make sense where there is a relatively dry carbon rich material and a useful market for products such as biochar, heat or fuel intermediates.

Gasification can work with suitably prepared carbon based feedstocks where the syngas can be usefully repurposed.

Combustion can be appropriate for large scale residual waste streams where recovery and recycling options have already been exhausted and there is energy demand.

Sometimes the best answer is not to build a waste to energy plant at all.

There may be more value in changing the production process, separating a material earlier, making it cleaner and moving it up the waste hierarchy.

Start with a view of the whole business

When looking at a potential waste to energy project, don’t start with a technology catalogue – ask these questions:

• What does the business already do and what skills does it have?

• How does waste to energy align with the business strategy?

• What other business activities could benefit?

• What materials are coming in and out?

• What energy does the operation consume?

  
  

The objective is to find where the strongest opportunities actually sit, then determine which solution makes sense, whether it is for wastewater recovery, waste treatment, energy production or cost minimisation.

Reach out if you are asking these questions too and lets see if I can help.