Waste thermal technology. What is it? Is this good for Malaysia?

Thermal Technologies, especially #wastetoenergy plants, have gained rapid traction as an effective #wastemanagement method. Alternative technology such as #wastepyrolysis have also attracted attention of late. This paper compare and contrast these two technologies. And explores the suitability of thermal technology for Malaysia in my personal opinion

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Thermal Technology for waste management. What are the key objectives?

Thermal treatment for waste management involves using high temperatures in the processing of wastes. The key objectives for this treatment include destruction of wastes including pathogens, significant reduction in waste volume and production of solid or gaseous inert products and energy valorization (Puna & Santos, 2010).

Waste is thermally treated either by adding sufficient amounts of air to achieve good combustion resulting in resulting in completely burned-out bottom ash and flue gas, or by maintaining an environment of air deficiency or absence of air, whereby the waste is pyrolised . The former refers to waste incineration and the latter, waste pyrolysis.

The key objectives for this treatment include destruction of wastes including pathogens, significant reduction in waste volume and production of solid or gaseous inert products and energy valorization        

Incineration is a popular disposal method among OECD countries. In 2016, 22% of the global wastes were diverted to incineration from the 2.01 billion tonnes of municipal solid waste (‘MSW’) generated worldwide. This method are primarily selected by high-income countries with high-waste capacity and land-constrained (Kaza, Yao, Perinaz, & Van Woerden, 2018). Japan and Singapore are the only two Asian countries among these high-income countries. Figure 1 shows the disposal method by four groups of countries.

Figure 1: Disposal methods by income levels (Kaza et al., 2018)

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Many countries with temperate climate require home heating often throughout the year. In Europe, waste which could not be recycled was recognized as a source of fuel for district heating and later, also combined heat and power (‘CHP’). In a 100-year commemorative account for waste incineration in Denmark, the factors such as political support to district heating and waste incineration, and coherent regulations in energy and waste management, were highlighted to have supported Denmark to meet the EU Landfill directive in 1999 requiring all wastes to be disposed of in landfill has to undergo prior treatment. Denmark was the first country in the world to ban on the landfilling of incinerable waste (Kleis & Dalager, 2007). By removing landfill as a disposal method (apart from products from waste incineration plants as bottom ash), most wastes are diverted to waste incineration.

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Waste Thermal Technology (1) - Waste Incineration

The waste incineration is the process of combustion, which is an exothermic process between fuel and oxygen (or air). The wastes acts as the fuel although fossil fuels may be co-fired. From the waste incineration, the principal gaseous products are carbon dioxide and water vapor. The solid residual are bottom ash from the combusted wastes in the combustion system, and soot particles and other contaminants from the flue gases captured in the Air Pollution Control (‘APC’) Systems.

Waste composition determines, in part, the composition of the ash and gas. Incineration can achieve the reduction in volume of wastes by up to 95% and in mass by 80-85%. Waste or feedstock preparation in reducing recyclables and homogenising using the overhead crane in waste pits help to achieve high rates.

Figure 2: Schematic diagram of a typical waste incineration process (Committee on Health Effects of Waste Incineration, Board on Environmental Studies and Toxicology, Commission on Life Sciences, & National Research Council, 2000)

In a typical waste incineration plant, wastes is prepared as feedstock to the combustion units, which are designed to achieve efficient combustion and reduced emissions. Optimal design and operation of the combustion unit takes into consideration of the 3Ts - incineration temperature, turbulence of the gas mixture being combusted, and gas-residence time at the incineration temperature. To achieve efficient combustion, the gas stream must reach sufficiently high temperature for a sufficient period of time with sufficient turbulence or mixture of fuel and oxygen in the combustion unit. The hot flue gas needs to be cooled before the gas goes through further cleaning. In many plants, energy recovery is an integral part of the waste incineration hence the name Waste-To-Energy (‘WTE’) plants. In these plants, the gas cooling is achieved with waste heat boilers producing steam for heat and / or energy recovery. The cooled gas is further cleaned off dust, particulates or other acidic pollutants in the APC systems. The cleaned flue gas is safe to be released to the atmosphere through a stack.

There are three main types of combustion units namely moving grate, rotary kiln and fluidised bed. Moving grates transport and agitate the feedstock into the combustion zone operating typically at temperatures around 900 – 1,100O C, to allow exposure of a large surface area of waste to air. For MSW, moving grate is by far the most selected technology for mass burning of co-mingled waste feedstocks. Extensive research in the West opined that mass burn incineration on a moving grate can be considered as the Best Acceptable Technology for MSW or co-mingled wastes (Kleis & Dalager, 2007; T. Rand, J. Haukohl, & U. Marxen, 2000; Themelis, 2008) although each waste incineration plant is site-specific and waste composition-specific, among others. Figure 3 is a summary of the advantages and disadvantage of the moving grate incinerator.

Figure 3: Main Advantages and Disadvantages of Moving Grate Incinerator (T. Rand et al., 2000)

Japan is the largest user of thermal treatment in the world for MSW – around 40 mil tonnes. Most of the plants are based on moving grates technology however there are around 100 plants which are based on novel technologies such as direct smelting, Ebara fluidised process and Themoselect-JFE gasification and melting technology process (Themelis, 2008). A factor which breeds innovation is the local legislation which do not allow transportation of “as is” MSW between municipalities. The novel technologies serve to pre-processed the waste (for example refuse-derived fuel) for further incineration in large WTE plants.

Japan is the largest user of thermal treatment in the world for Municipal Waste.A factor is the local legislation which do not allow transportation of “as is” MSW between municipalities.        

Similarly, in China, WTE plants are favoured due to land constraint and a more developed economy for cities. In just 5 years (2001-2005), a total of 55 incinerators were built based on moving grate technology and fluidised-bed technology, with incineration capacity of 12% of China’s MSW generation. The table below shows the distribution of the plants where more moving grate technology were imported for larger capacity plants, whereas the localization of the fluidised-bed technology were successful.

?Although previous research pointed that fluidised–bed incinerators have been less popular because waste pre-treatment by shredding is often necessary making the operations expensive and complicated (T. Rand et al., 2000), its popularity in China have been rising rapidly due to the success in localisation the technology which has advantages in lower capital costs and its high tolerance for high-moisture and low calorific value (‘CV’) MSW (Chen & Christensen, 2010). To make up for the waste with CV as low as 5000 MJ/kg, coal of up to be 15% of the total waste can easily be added to the waste feedstock in fluidised-bed incinerators but not in moving grate incinerators. Favourable policy in energy pricing from WTE (7-9 cents/kwH) considered as renewable energy as compared to coal-fired power plants (4-6 cents/ksH) also pushed the use of fluidised-bed technology. The growth of thermal technologies are expected to continue rapidly with key reasons for energy recovery, land scarcity for landfills and outright government support for WTE (Themelis, 2008). An overview of the WTE plant is in Figure 4 below.

Figure 4: Incineration technology overview – by key processes (T. Rand et al., 2000)

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Waste Thermal Technology: (2) Waste Pyrolysis

The waste pyrolysis is the thermochemical decomposition of organic material at high temperature in the absence of oxygen. Gasification uses only a fraction of oxygen and operates at a higher temperature. Unlike incineration, it is an endothermic process and has a lower operating temperature and lower emissions of air pollutants. The wastes acts as the fuel which can be converted and optimized to generate a combination of solid (ash, char), liquid (oil, wax, tar) and gaseous products (syngas or combustible gas) which are considered relatively of high value, high yield and available for storage (for solids and liquids). The generation of the products can be achieved in different proportions by varying the operating parameters such as temperature or heating time. Similarly to incineration, the syngas require cooling down and cleaned in the APC Systems followed by released of cleaned air to the atmosphere.

The process of pyrolysis have been well established in large scale plants for homogenous feedstocks such as biomass (for recovery of bio-oil) and to a smaller extent, waste tires (for recovery of steel, oil and syngas) (M. Ringer, V. Putsche, & Scahill, 2006). The capacity of pyrolysis plants are flexible and smaller, when compared to the high capacity waste incineration plants. There is a wide variety of furnace or reactor designs such as fluidised-bed, circulating fluidised-bed, rotating cone, vacuum and others. Figure 5 is a list of some of the large-scale biomass pyrolysis plants worldwide.

Figure 5: Examples of biomass pyrolysis operating plants worldwide (M. Ringer et al., 2006)

With the emphasis towards resource management, traditional waste management methods like landfilling and incineration have been considered outdated. Certain studies highlighted pyrolysis to be modern, effective and easy-to-operate solutions (D. Czajczyn et al., 2017).

However, waste pyrolysis for MSW have only attracted attention of late with regards to improvement management of resources. In the early 1990s, the Europe market started to reconsider alternative technologies other than incineration due to its political desire to develop such technologies. Since then, there has been limited successful plants and more so for stand-alone process such as the Waste Pyrolysis Plant in Burgau, Germany. Figure 6 shows the waste processes of the Burgau Plant.

Figure 6: Schematic of the Waste Pyrolysis Plant in Burgau, Germany (Quicker, 2016)

Operating since 1986, the Burgau Plant is the only large scale pyrolysis plant still in operation. It has a capacity of 2 lines of 3 tons per hour furnace with a 2.2 MW CHP unit. The key process are pre-shredding, pyrolysis at operating temperature of 470 °C – 500 °C and syngas combustion at 1,250°C - 1,300° C. The waste feedstocks are household wastes, bulky wastes from household and sewage sludge. The waste feedstock is a co- treatment of sewage sludge contaminated with chrome hence the low temperature pyrolysis process avoids the formation and release of chrome (IV) and heavy metals. ?It was reported that there is still a big challenge to make pyrolysis economically viable (Gleis, 2015).

In China, there has been an increase of interest in pyrolysis in smaller cities and towns to reduce the long-distance transportation and the increasing difficulty to find new incinerators and landfills sites. While incineration plants require high capital cost and assurance of environmental safety, suitable sized pyrolysis plants with energy products output is an attractive option. A recent study of pyrolysis process for different fractions of MSW in China found that pre-treatment is a necessary step and that includes separation of undesirable materials, size reduction, sometimes drying to reduce moisture of feedstock. Study found that different products were generated at temperatures ranging from 500 to 900O C using a mixture of kitchen waste, paper, cloth, bamboo, plastics and glass. Further, the heating value of char also increased with increasing temperature from 18.3 MJ/kg at 500O C to 30.4 MJ/kg at 900O C (Chen, Yin, Wang, & He, 2014). Figure 7 explained the yield of the pyrolysis products.

In China, interest is increasing in pyrolysis in smaller cities and towns to reduce the long-distance transportation and due to increasing difficulty to find new incinerators sites and landfills sites        

Figure 7: Yields of product from MSW pyrolysis (Chen et al., 2014)

Comparison of incineration technology and pyrolysis technology

The waste thermal technologies such as waste incineration and waste pyrolysis (and gasification) are suitable dependent on a wide variety financial, environmental and social factors in addition to the objectives that is desired to be fulfilled. Figure 8 is a summary of the technology and products from these technologies.

Figure 8: Comparison between waste thermal technologies?(Dong et al., 2018)

Waste incineration, WTE plants in specific, has been on a sharp growth trend. In China, it has been reported that over 430 WTE plants are under operation at end of 2019 with a total incineration capacity of 450,000 t/d representing 70% of the country’s MSW. Landfill regulations in Europe will spur the growth as EU members will only be permitted to dispose no more than 10% of their MSW to landfills (Yan, Agamuthu P, & Waluyo, 2020). Hence, the waste incineration technologies will continue to develop.

In China, over 430 WTE plants are under operation at end of 2019 with a total incineration capacity of 450,000 t/d representing 70% of the country’s MSW. In Europe, EU members will only be permitted to dispose no more than 10% of their MSW to landfills which will spur thermal treatments to be used        

On the contrary, waste pyrolysis can be considered at an early stage of development when compared to waste incineration. Not only the technology, many aspects including the regulations and frameworks encouraging pyrolysis as a sustainable waste disposal methods are still under study. ISVAG, the Dutch Inter-municipal for Sludge and Waste Disposal of Antwerp Municipalities reported in a high level meeting that waste technologies like pyrolysis could only be sustainable with specific preferential regulations from the government, for specific waste fractions and connectivity with other thermal plants to optimise the pyrolysis products would be important. On the other hand, the development of waste incineration technologies have reached the state-of-the-art for the treatment of non-homogenous MSW (Quicker, 2016).

?In my opinion, is Malaysia ready for waste thermal treatment technology?

The case for thermal technology shall inevitably be considered in relation to the alternatives available along with the objectives which are desired. The pillars of economic, ecological and social acceptance ought to ultimately guide us to the sustainable disposal method.

In the following, I set out a discussion on the two fractions of wastes along with my preferred method of treatment for them:

1.?????Hazardous waste and medical wastes

Incineration technology has been a key process in the treatment of #hazardouswastes and #medicalwastes (currently these wastes are not included in the category of MSW in Malaysia). The high temperatures of incineration destroy pathogens and toxic contamination in order to make the residues inert for landfilling. In my opinion, thermal technology is the preferred treatment method. Malaysia adopted this method ahead of many Asian countries, apart from Singapore and Japan. Infrastructures such as the existing incineration plants do also require dynamic and strategic thinking which will continue to evolve with times.

Thermal technology is the preferred treatment method for hazardous and medical wastes. Malaysia has adopted this method ahead of many Asian countries.        

In current times as we face a pandemic, there has been little or no discussions on the management of disposable face masks which potentially be infectious to the detriment of our sanitary workers. Such items ought to be considered as medical wastes and be segregated from the household wastes as similar calls have been sounded in other countries (Rongmeng & Jianguo, 2020).

2.?????Municipal solid wastes

Malaysia’s overall waste generation in 2012 from households and industry, commercial and institutional (‘ICI’) was 33,130 tonnes per day with majority of 84% from Peninsular Malaysia and balance from East Malaysia (Jabatan Pengurusan Sisa Pepejal Negara, 2013). Figure 9 below shows the generation in accordance to Urban and Rural for the respective areas. Figure 10 and 11 shows the national waste composition for household and ICI respectively.

Figure 9: Waste generation from households and ICI in Peninsular and East Malaysia?(Jabatan Pengurusan Sisa Pepejal Negara, 2013)

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Figure 10: Malaysian household waste composition

Figure 11: Malaysian ICI waste composition

Based on the latest published waste data above, it is useful to adopt the widely accepted waste management hierarchy, one agreed by the parties to the Basel Convention, which states that it ‘encourages treatment options that deliver the best overall environmental outcome, taking into account life-cycle thinking’. Figure 12 shows this hierarchy. In the context of Malaysia, it is imperative and urgent that we take immediate steps to move towards zero "uncontrolled disposal" which refers to dumpsites.

Figure 12: Waste management hierarchy (Wilson et al., 2015)

We need to ensure that wastes collected are disposed properly and all existing disposal sites receiving the wastes to be environmentally safe. Todate only 15% of the 146 active landfills in Malaysia can be considered #sanitarylandfill whilst rest are #dumpsites with high impacts to the adjacent communities and to the environment. Further, many have short remaining life spans (Leoi, 2019). Even as finding suitable sites for new landfills become more difficult, landfill may still remain as a key waste disposal option as it is the cheapest option. Disposal at dumpsite or landfill costs RM35/tonne,?as?compared?to RM500/tonne?for?incineration?and?RM216/tonne?for?composting (Fauziah, C. Simon, & Periathamby, 2004). Landfill inevitably will remain a core technology which we must ensure it to be safe by upgrading the existing or build new sanitary ones.

Given the high food waste content in the household and ICI disposed, this is an opportunity to carefully implement useful management and employ biological technologies such as anaerobic digestion or composting technologies to reduce its volume and gain useful by-products, and also avoid it being dumped without any treatment at risk of production of methane generation. Strategies set out by FAO to reduce food loss and waste reduction should be given consideration by the policy makers (FAO, 2019).

There are alternative methods in MSW management suited to Malaysia's context and thermal technology is a method to be considered in accordance to our national affordability levels. 
        

In contrast, the Minister of Ministry of Housing and Local Government made an announcement that each state in Malaysia will have at least one WTE plant by 2020. The objective was to move away fro MSW disposal sites ans such no longer need to open new disposal sites in the future (MIDA, 2018). Thus far, no plant has been commissioned. The first WTE plant with mechanical segregation systems with capacity of 600 tonnes is being built. Sited in Negeri Sembilan, the plant is reported to be able to produce between 20MW and 25MW of build-operate-manage-transfer basis for 25 years have been delayed (Azizi, 2019). The success of thermal technologies will ultimately depend on the strength of our institutions and #governance , policy structure in waste and energy management and our affordability levels.

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