Waste Incineration

Alex Skaria, Director, Engineering and Marketing, Thermal Power, Pöyry

Introduction

Asia’s growing economies will generate increasing amounts of waste which requires a proper and environmentally safe disposal. According to the World Bank, Municipal Solid Waste (MSW) generation is going to double by 2025, keeping in mind that OECD countries are still producing the majority of that waste. In Asia, the current average waste generation is approximately 0.9 kg/capita/day and is set to increase to 1.5 kg/capita/day as the economy develops. The current waste production in Asia stands approximately at 738,000 ton/day and will increase to 1,865,000 ton/day in 2025. The waste disposal in this region will be one of the major challenges in the years to come.

Waste incineration is not a low-cost technology and investment in this technology should be targeted carefully. MSW incineration should only be applied to waste which cannot be recycled in a way that creates usable products and at the same time eliminate pollution. In other words you don’t want to spend money to burn products which could be used or sold elsewhere.

That said, if a recycling process generates in itself harmful waste or products which have no market value (e.g polluted compost, mixed waste as residue of the RDF separation) and as a result these residues need to be landfilled, it is preferable to directly incinerate MSW since incineration maximizes the reduction of waste and destroys pollutants and plastics before they get distributed in the environment.

Redistribution of waste is a major concern. In particular plastic pollution and micro-plastics is recognized as a major problem worldwide. Several scientists have argued that we are now living in an anthropocene or an “Age of Plastic” as our plastic waste leaves noticeable traces on rock layers of mountain tops to deep ocean floors and can be fossilized into the far future. Not to mention the yet unknown risks of plastic entering our food chain.

Methane emissions from biomass in landfills contribute to the greenhouse gas effect to a larger extent than potential carbon dioxide emissions resulting from incineration. Furthermore, uncontrolled burning of waste on landfills, which happens more often than not, emit uncontrolled Dioxins and Furans in high concentrations, those exact components which are often raised as main argument against MSW incineration.

In summary waste disposal in landfills, scavenging for waste separation and partial waste incineration without proper segregation cannot be the solutions for the growing waste generation worldwide and in particular in Asia.

Citarum River, flowing to the Sea, is the main source of household water for Jakarta. (14million people). Photo source: photobucket.

Waste Reduction through Separation at the Landfill

Many proponents argue that waste reduction through separation and recycling of waste is an effective method to reduce waste. While it does allow for some plastics, metal, and paper to be recycled, the majority of waste still remains in the landfill.

Waste separation processes after collection of waste, such as they are currently applied in Asia, leave a final residue which still needs to be landfilled and in my point of view are therefore not a sustainable solution. The plastic residues are not fully removed from the final residue and this final product is still a potential polluter through uncontrolled burning, methane fermentation and leaching of chemicals. Therefore alternative ways of waste management should be considered and many European countries have good examples how this can be managed.

Waste Reduction at the Source- A strong case for Separate Waste Collection

As mentioned in the introduction, waste incineration is not a low-cost technology and it is important to only treat waste which has no further usage. Furthermore a waste incinerator has technical limitations what it can burn, in particular with regard to the calorific value of waste. The higher (also with certain limitations) the calorific value of waste, the more efficient the combustion process and the more cost-efficient the investment. In order to get reasonably high calorific value for MSW it is important to reduce moisture and organic material.

Organic material is in most cases introduced as vegetable and food waste. Vegetable and garden waste are large contributors to moisture, and moreover are much more efficiently treated in a composting plant instead of a waste incineration, hence it would be prudent to collect this type of waste separately which at the same time makes it a more valuable resource. While it is true that it is very difficult to force households to start a separate bio-waste collection, it can be a relatively easy start to collect this waste separately in fresh markets and shopping malls. These facilities could supply sufficient amount of organic waste to justify the development of a composting plant. Organic waste which is correctly collected and not mixed with other hazardous waste like plastic, batteries, glass, etc. will have a market value. Once people notice the benefit of such a system the government or municipalities should promote this kind of separate collection through education and/or economic incentives combined with expansion of separate collection centers in certain cities or districts.

Other waste streams could be collected similarly in larger shopping malls, e.g. PET bottles, aluminum cans, glass bottles etc. through dedicated collection points as is done in many European cities.

Currently, the waste in most Asian countries is separated at the landfill site, after it has been collected. That results in polluted fractions for all waste streams, e.g. organic waste is polluted with plastics and batteries, plastic is polluted with food, etc. and as a result none of the fractions really have a proper market value. As an example, one single battery in one ton of organic waste makes it unsuitable as soil enhancer or compost because it exceeds the limitations for heavy metals and so most likely unsold compost will end up back in the landfill.

After having collected organic waste and other recyclable waste, the remaining waste cannot be utilized or recycled and should be incinerated. The advantage of this system is that:

a)The recyclable products are collected separately in relative clean fractions

b)The amount of waste to be incinerated gets reduced

c)The calorific value of the MSW to be incinerated improves significantly

All good reasons to introduce such a system. But it requires the Governments to take up the initiative and introduce suitable policies. This system does not develop by itself and no private developer can introduce it on a large scale on his own.

Waste Incineration MSW vs RDF

Several developers and suppliers promote RDF as opposed to MSW incineration because the fuel has better quality, less moisture, and thus higher calorific value. Nonetheless, from the reasons I mentioned above, RDF is not a final solution for the waste treatment as long as there is no separate waste collection system, simply because it treats only one part, the best part, of the waste stream and a large portion of the residue, containing plastics and other pollutants is left to be landfilled.

Most Asian countries allocate their budgets mainly for waste collection and only a minor portion for waste treatment. Some Asian countries try to circumvent this budgetary problem by inviting private developers to build Waste to Energy (WtE) plants and giving an incentive for the electricity sold. That forces the developers to optimize the power plant and most importantly fuel efficiency because payment is made for generating electricity as opposed to getting rid of the waste e.g. through a tipping fee. This approach defeats the purpose of eliminating the waste and as a result many private developer in these schemes resort back to using RDF or pure industrial waste instead of MSW which then brings us back to the initial problem that not all waste is properly disposed.

MSW incineration should be a solution that makes landfilling obsolete. Hence in absence of a systematic and separate waste collection for biodegradable waste, direct MSW incineration is in my view the preferred method of waste treatment. It ensures that no plastic residues and other polluting residues are spread in the environment.

The other argument against MSW incineration is the formation of dioxins and furans. The technologies to limit emissions of these toxins have been developed and applied successfully over the past decades. The majority of MSW incineration plants in Europe demonstrate that both dioxins and furans can be removed from the flue gas to levels below 0.1 ngTEQ/Nm3, well in line with World Bank and EU standards.

RDF works well in countries which have a well-developed separate waste collection or in cases where remote areas send their waste to a central MSW incineration plants and are forced to reduce the volume by producing RDF. In absence of such a separate waste treatment or remote plant, direct MSW incineration should be the preferred solution.

Waste Incineration vs Gasification

Back at the end of last century gasification of waste was introduced into the markets in Europe as being the magic bullet for MSW treatment. The main difference between incineration and gasification is the formation of a syngas under sub-stoichiometric conditions, i.e. under very low oxygen content. The syngas is then burnt in a separate chamber at high temperatures. Some other, more exotic processes use this syngas to produce oil. The main argument was lower amount of flue gas due to lower excess oxygen and the fly ash being molten at high temperatures and crystallized to glass, thus keeping all heavy metals and pollutants locked in this glass. Examples of such technologies were the much-praised Thermoselect process, the JFE Process and a Siemens KWU Schwarze Pump Process. Only a very limited number of projects primarily using a very selective RDF have been operated in Europe with mixed success and many plants closed down operation. Some of the technologies were bought by Japanese companies and built in Japan. The driving force was the high cost of final landfilling of the fly ash but even so, most of these plants in Japan have stopped operation. Main problems are plant low reliability, formation of tar which requires regular cleaning, high operation cost, and as far as we are aware,currently only one new plants is being planned (using pre-treated RDF) in UK. No new plants are planned or built neither in Japan nor in Europe.

As for the future in Asia MSW gasification is not a viable solution. It has not really proven to be economically viable on a large scale. Furthermore the main argument in favor of gasification, landfill cost for ash is not really applicable, because landfilling cost for fly ash is still cheap. Environmentally none of these technologies have proven to be superior to direct MSW incineration..

MSW Stoker Incinerator vs Circulating Fluidized Boiler (CFB)

CFB technology is praised by some suppliers as the preferred technical solution for MSW treatment. In cases where the developer has chosen RDF as fuel this technology is indeed suitable. However, it needs to be pointed out that for the reasons I have mentioned above RDF production from waste is not a sustainable solution for waste disposal. CFB technology has much more limited fuel flexibility compared to stoker incinerators. Not only is fuel calorific value limited but also fuel size, since all fuel needs to be shredded before it enters the incinerator.

As a general guideline, the most flexible technology which allows MSW to be treated directly without any further pretreatment is the stoker or step grate MSW incinerator. It is for this very reason why over 90% of all plants in Europe and Japan are based on this technology.

Conclusion

Efficient and effective waste disposal requires a government level policy which takes a holistic approach into account. The goal should be the reduction of waste through separate waste collection, efficient recycling of waste, biological treatment of organic waste and incineration of residual waste.

RDF preparation from waste and RDF incineration is a measure applied to improve the economics of incineration mainly due to lack of proper waste policies. It does not provide a solution to get rid of MSW landfills.

Waste gasification is a technology with some limited applications in Japan but it has not been successfully operated in any European country where the vast majority of MSW treatment is based on stoker incineration.

Modern MSW incineration technologies, if properly designed and operated are safe and emissions of pollutants are controlled. Dioxin and Furan emissions are kept with the limits set by the EU and World Bank.