**1. Introduction**

This chapter deals with the possibilities of making use of municipal solid waste (MSW) in combined gasification systems with coal to help solving two situations. One is the need for a more sustainable use of highly available coal resources and the other is the need for a more sustainable handling of domestic solid wastes, which are not properly disposed. When these two combine, as is the case for a country like Colombia, there are real spaces for the use of waste to energy technologies.

Coal is an abundant resource in many places of the world. Unfortunately, the combustion of coal has been clearly associated with the generation of CO2 and global warming, which has caused a tendency to gradually abandon coal as an energy resource, preferring natural gas and renewable energy. This is a worrying situation for a country like Colombia, which possess very large coal deposits. Currently, this country is exporting large amounts of coal and this contributes largely to the generation of income. In this sense, it is important to find applications for coal, both in chemical process and more sustainable energy systems and also develop ways for CO2 recovery and conversion that allow for the continuous use of coal.

The waste problem is very important in developing countries like Colombia [1]. With 49 million people in 2017 and its population mostly concentrated in the Andean highlands and along the Caribbean coast, it has 31 cities of more than 200,000 habitants and 65 with more than 100,000; being one of most urbanized countries in the region, its urban population is estimated at 76%. Informality and poverty are big problems, and these come associated with informal waste recycling practices. With a medium generation of 0.54 kg/hab./day, the estimated daily generation is around 26,000 tons. Colombia is a model in the region in the recycling of paper and cardboard, with a recovery of 57%. This has to do with the existence of industrial

plants able to use these materials in their process, which has favored a well-organized recycling scheme. Currently in the country, the recycling rate of waste such as paper, cardboard, glass, metals, and plastics is 17%, and by 2019, the goal will be to achieve a recycling target of 20% as a result of the implementation of regulatory instruments in the public cleaning services and the tariff frameworks, processes that the national government advances. The rest of the waste goes to waste dumps or sanitary landfills as there are not any thermal treatment facilities in the country. Very few of the landfills facilities have water lixiviate treating plants or methane burning systems. Space is becoming an issue and there are growing concerns and limitations about the growth of the landfill system areas in the coming years. In other cases, environmental concerns are becoming more and more important [2–5].

Waste to energy systems are very important for the sustainable disposition of municipal waste as has been consistently shown in developed countries. This has to do with available technology. In general, in developing countries, there is lack of companies that can manufacture equipment for thermal treatment systems capable of handling hundred or thousand tons per day of mixed waste, burning them in a controlled way, generating electricity, and controlling the air pollution problems related to this. This means that local responsible waste-handling entities will tend to look for solutions with external providers and this means usually very high initial investments. As shown in the case of China and India, this can be changed, creating competitive sectors in the WtE technology, able to confront their own situations and to export technology and equipment.

Engineering and design are very important components of the necessary technology for the development of WtE (waste to energy) systems in a country. Implementing these systems requires detailed studies and planning activities and it is advisable to do the projects considering all the engineering stages. There is always the temptation and the idea that the projects can be accelerated and put into place based on the experience and support of suppliers and makers, by means of EPC developments. The idea being that in such a way, the engineering stages can be simplified or even avoided. This normally is a much costlier and rigid solution and does not contribute to developing local technology and desired prosperity. In the solution of the problems, there is ample space to develop a region, as compared to relying only on externally provided solutions.

One of the most important stages is the development of conceptual studies and engineering based as much as possible on local expertise, duly backed, of course with external experience and support. The authors are part of an international working group known as WTERT supported by Earth Institute at Columbia University [6]. The Waste to Energy Research and Technology Council (WTERT) brings together engineers, scientists, and managers from universities and industries worldwide and the authors belong to the Colombian chapter, which is supported by ACIEM (Engineering Colombian Association). WTERT tries to identify and advance the best available waste to energy technologies for the recovery of energy or fuels from municipal solid wastes and other industrial, agricultural, and forestry residues. The authors are also project engineers at HATCH, an international engineering company, and have experience in waste to energy systems for industrial applications.

As part of their work, they participated in a project aimed at using gasification systems based on the co-combustion of coal with biosolids coming from a municipal water treatment system [7–9]. This chapter considers using this technology for waste to energy systems applied to municipal solid waste (MSW). It reviews the situation in this field. This, in order to explore the basis for an alternative based on co-combustion with coal for generating syngas in small- or medium-sized municipalities, produces less than 200 tons of waste per day. It develops a theoretical

**5**

*Waste to Energy and Syngas*

on the co-gasification agent.

Greek electricity market [13].

6.5, and 6.7 MJ/Nm3

Nm3

*DOI: http://dx.doi.org/10.5772/intechopen.85848*

model applied to the specific case of municipal waste similar to the one generated at the city of Medellin, where the authors work, co-gasified with available local coal. Gasification processes involve the reaction of carbonaceous feedstock with an oxygen-containing reagent, usually oxygen, air, steam, or carbon dioxide, generally at temperatures in excess of 800°C. It involves the partial oxidation of a substance which implies that oxygen is added but the amounts are not sufficient to allow the fuel to be completely oxidized and full combustion to occur [10]. The main product is syngas, which is a mixture of gases including CO and H2, which can be used to produce fuels and chemicals, or be burned to generate heat or electricity. Some

The basics of the gasification process can be found in many publications and books. MSW gasification has been an object of many studies also and the process details and specificities have been compiled and documented. Zafar [10] shows the qualitative basics, advantages, and disadvantages, as well as classifications depending on the technology, feedstock, and reactors, focused on municipal solid waste. Arena [11] presents a deeper treatment of the gasification technology, the chemistry, reactor and technology description and comparison, and environmental aspects. In his thesis, Klein [12] also analyzes these aspects in depth and also consid-

ers investment and operative costs with data of operating plants at that time.

In terms of co-gasification, specific studies have been carried out showing the technical feasibility of the technique, and quantifying the improvements depending

Koukouzas et al. analyzed co-gasification of MSW with coal. They evaluated the techno-economic feasibility, of a 30-MW (e) co-gasification power plant based on integrated gasification combined cycle (IGCC) technology, using lignite and refuse-derived fuel (RDF), in the region of Western Macedonia, Greece. The preliminary cost estimation indicated that this plant was not profitable, due to high specific capital investment and in spite of the lower fuel supply cost. The estimated cost of electricity was not competitive, compared to the dominating prices for the

Hu et al. studied a three-stage system for co-gasification of MSW with high-alkali

internal combustion engines. They concluded that high-quality syngas can be pro-

nation and catalytic tar cracking action of high-alkali coal char at a low cost [14]. Co-gasification of MSW with switchgrass cuttings, by means of a small commercial-scale downdraft gasifier (100 kg/h), indicates that co-gasification of up to 40% MSW performed satisfactorily. The heating values of syngas were 6.2,

same cases, the cold and hot gas efficiencies were 60.1, 51.1, and 60.0% and 65.0, 55.2, and 64.4% [15]. Eghtedaei et al. also analyzed co-gasification with biomass and

in the final ash quality and the gas emissions without important changes in the

Enerkem has effectively developed its own process to obtain methanol and ethanol from MSW through gasification and has an operating plant in Alberta,

The co-gasification with the bottom ash has been studied, finding improvements

These few examples show that in principle, not only MSW gasification, but also co-gasification are feasible at different scales, including commercial scale. Many companies or institutes have developed their own process routes with particularities to be more efficient or suitable for the feedstock. In addition to the studies

and HCl to 17.6 mg/

, meeting the intake-gas conditions for

/kg from three-stage gasifier, due to dichlori-

for co-gasification ratios of 0, 20, and 40%, respectively; in the

by-products are ash and tars depending on the technology used.

coal char. Tar content was controlled to as low as 11.3 mg/Nm3

. Lower heating value attains 12.2 MJ/Nm3

found an improvement in the H2 concentration [16].

reviewed, some other successful cases could be considered.

duced at a steady yield rate of 1.57 Nm3

operability and syngas quality [17].

#### *Waste to Energy and Syngas DOI: http://dx.doi.org/10.5772/intechopen.85848*

*Sustainable Alternative Syngas Fuel*

plants able to use these materials in their process, which has favored a well-organized recycling scheme. Currently in the country, the recycling rate of waste such as paper, cardboard, glass, metals, and plastics is 17%, and by 2019, the goal will be to achieve a recycling target of 20% as a result of the implementation of regulatory instruments in the public cleaning services and the tariff frameworks, processes that the national government advances. The rest of the waste goes to waste dumps or sanitary landfills as there are not any thermal treatment facilities in the country. Very few of the landfills facilities have water lixiviate treating plants or methane burning systems. Space is becoming an issue and there are growing concerns and limitations about the growth of the landfill system areas in the coming years. In other cases, environmen-

Waste to energy systems are very important for the sustainable disposition of municipal waste as has been consistently shown in developed countries. This has to do with available technology. In general, in developing countries, there is lack of companies that can manufacture equipment for thermal treatment systems capable of handling hundred or thousand tons per day of mixed waste, burning them in a controlled way, generating electricity, and controlling the air pollution problems related to this. This means that local responsible waste-handling entities will tend to look for solutions with external providers and this means usually very high initial investments. As shown in the case of China and India, this can be changed, creating competitive sectors in the WtE technology, able to confront their own situations

Engineering and design are very important components of the necessary technology for the development of WtE (waste to energy) systems in a country. Implementing these systems requires detailed studies and planning activities and it is advisable to do the projects considering all the engineering stages. There is always the temptation and the idea that the projects can be accelerated and put into place based on the experience and support of suppliers and makers, by means of EPC developments. The idea being that in such a way, the engineering stages can be simplified or even avoided. This normally is a much costlier and rigid solution and does not contribute to developing local technology and desired prosperity. In the solution of the problems, there is ample space to develop a region, as compared to

One of the most important stages is the development of conceptual studies and engineering based as much as possible on local expertise, duly backed, of course with external experience and support. The authors are part of an international working group known as WTERT supported by Earth Institute at Columbia University [6]. The Waste to Energy Research and Technology Council (WTERT) brings together engineers, scientists, and managers from universities and industries worldwide and the authors belong to the Colombian chapter, which is supported by ACIEM (Engineering Colombian Association). WTERT tries to identify and advance the best available waste to energy technologies for the recovery of energy or fuels from municipal solid wastes and other industrial, agricultural, and forestry residues. The authors are also project engineers at HATCH, an international engineering company, and have experience in waste to energy systems for

As part of their work, they participated in a project aimed at using gasification systems based on the co-combustion of coal with biosolids coming from a municipal water treatment system [7–9]. This chapter considers using this technology for waste to energy systems applied to municipal solid waste (MSW). It reviews the situation in this field. This, in order to explore the basis for an alternative based on co-combustion with coal for generating syngas in small- or medium-sized municipalities, produces less than 200 tons of waste per day. It develops a theoretical

tal concerns are becoming more and more important [2–5].

and to export technology and equipment.

relying only on externally provided solutions.

**4**

industrial applications.

model applied to the specific case of municipal waste similar to the one generated at the city of Medellin, where the authors work, co-gasified with available local coal.

Gasification processes involve the reaction of carbonaceous feedstock with an oxygen-containing reagent, usually oxygen, air, steam, or carbon dioxide, generally at temperatures in excess of 800°C. It involves the partial oxidation of a substance which implies that oxygen is added but the amounts are not sufficient to allow the fuel to be completely oxidized and full combustion to occur [10]. The main product is syngas, which is a mixture of gases including CO and H2, which can be used to produce fuels and chemicals, or be burned to generate heat or electricity. Some by-products are ash and tars depending on the technology used.

The basics of the gasification process can be found in many publications and books. MSW gasification has been an object of many studies also and the process details and specificities have been compiled and documented. Zafar [10] shows the qualitative basics, advantages, and disadvantages, as well as classifications depending on the technology, feedstock, and reactors, focused on municipal solid waste. Arena [11] presents a deeper treatment of the gasification technology, the chemistry, reactor and technology description and comparison, and environmental aspects. In his thesis, Klein [12] also analyzes these aspects in depth and also considers investment and operative costs with data of operating plants at that time.

In terms of co-gasification, specific studies have been carried out showing the technical feasibility of the technique, and quantifying the improvements depending on the co-gasification agent.

Koukouzas et al. analyzed co-gasification of MSW with coal. They evaluated the techno-economic feasibility, of a 30-MW (e) co-gasification power plant based on integrated gasification combined cycle (IGCC) technology, using lignite and refuse-derived fuel (RDF), in the region of Western Macedonia, Greece. The preliminary cost estimation indicated that this plant was not profitable, due to high specific capital investment and in spite of the lower fuel supply cost. The estimated cost of electricity was not competitive, compared to the dominating prices for the Greek electricity market [13].

Hu et al. studied a three-stage system for co-gasification of MSW with high-alkali coal char. Tar content was controlled to as low as 11.3 mg/Nm3 and HCl to 17.6 mg/ Nm3 . Lower heating value attains 12.2 MJ/Nm3 , meeting the intake-gas conditions for internal combustion engines. They concluded that high-quality syngas can be produced at a steady yield rate of 1.57 Nm3 /kg from three-stage gasifier, due to dichlorination and catalytic tar cracking action of high-alkali coal char at a low cost [14].

Co-gasification of MSW with switchgrass cuttings, by means of a small commercial-scale downdraft gasifier (100 kg/h), indicates that co-gasification of up to 40% MSW performed satisfactorily. The heating values of syngas were 6.2, 6.5, and 6.7 MJ/Nm3 for co-gasification ratios of 0, 20, and 40%, respectively; in the same cases, the cold and hot gas efficiencies were 60.1, 51.1, and 60.0% and 65.0, 55.2, and 64.4% [15]. Eghtedaei et al. also analyzed co-gasification with biomass and found an improvement in the H2 concentration [16].

The co-gasification with the bottom ash has been studied, finding improvements in the final ash quality and the gas emissions without important changes in the operability and syngas quality [17].

These few examples show that in principle, not only MSW gasification, but also co-gasification are feasible at different scales, including commercial scale. Many companies or institutes have developed their own process routes with particularities to be more efficient or suitable for the feedstock. In addition to the studies reviewed, some other successful cases could be considered.

Enerkem has effectively developed its own process to obtain methanol and ethanol from MSW through gasification and has an operating plant in Alberta, Canada [18]. Mitsubishi Heavy Industries has a medium-sized plant in Kushiro, Japan, which has been operating since 2006, processing 240 T/day of MSW (2 units × 120 T/day), producing 4.6 MW of electricity. Their technology includes an ash melting system that improves the ash quality and controls the dioxin emissions [19]. Currently, Fulcrum-Bioenergy is preparing the construction of a MSW gasification facility in Nevada (USA) to produce 10 million gallons a year of biofuels [20]. Aries Clean Energy has different facilities already working in the USA. In Sanford, Florida, they installed a fluidized bed gasification plant for 30 T/day biosolids from a sewage treatment plant [21]. In Lebanon, Tennessee, a downdraft reactor gasifies 64 T/day of biomass to produce heat that is used with organic Rankine cycles (ORCs) [22]. The same technology was used in Covington, Tennessee, with a reactor of 12 T/day mixture of wood residues and sludge moving a 235-kW ORC [23]. In Boral Bricks, Alabama, 12 modular downdraft systems were used to process residual wood to produce syngas to be burned in brick furnaces [24].

Tanigaki et al. have reviewed the operation of two plants in Japan. They reported more than 46 gasification facilities working nowadays in Japan but focused on the two more recent ones, one processes MSW with higher operating hours and lower consumables in Japan. The other one is focused on its waste flexibility, processing not only MSW but also IBA, rejects from recycling center, and sewage sludge. They show the reliability of these plants as well as their effectiveness on the MSW treatment, energy efficiency, and accomplishing environmental requirements [25].

There are many gasification facilities in the world. A good review of them can be found in the Worldwide Syngas database of the Global Syngas Technology Council [26]; here, the facilities can be located and filtered by feedstock, product, and technology among others. In the following studies, in addition to very good technological reviews of the MSW thermal treatment, especially on gasification, there are sets and lists of plants, facilities around the world with their capacities and owners.


There can be found good examples of feasible and working projects for MSW treatment; however, it is important to note that these projects have specific and contextual difficulties. Hakan Rylander, an experienced actor in WtE, is a bit skeptical about gasification of MSW, mostly because of the heterogeneity of the feedstock, and because the energy balance sometimes has turned out to be negative [33]. Also, Tangri and Wilson [34], make an interesting risk analysis of the gasification and pyrolysis of MSW. They conclude that "the potential returns on waste gasification are smaller and more uncertain, and the risks much higher, than proponents claim," "Technical and economic challenges for gasification projects include failing to meet projected energy generation, revenue generation, and emission targets. Gasification plants also have historically sought public subsidies to be profitable." At the end of

**7**

**Table 2.**

**Table 1.**

*Coal properties considered [35].*

*MSW properties considered [35].*

*Waste to Energy and Syngas*

chemicals.

**generate syngas**

*DOI: http://dx.doi.org/10.5772/intechopen.85848*

world that have stopped operations.

the document, there is a list of ten notable cases of plants and facilities around the

**2. Modeling of municipal solid waste and coal co-combustion to** 

This section develops a theoretical model applied to the specific case of municipal waste. The basic information for this is the composition of the MSW and of the coal to be used, plus their heat powers. **Tables 1** and **2** show the data used. These tables have been prepared by authors based on several studies made during their work with coal boilers and power plants at Colombia. Two cases are considered for the waste. In the first one, waste as currently generated, the average quality of the MSW is considered in the city of Medellin, which is quite rich in organic materials and, so, very high in water content. In the second case, previously separated waste is

Water content % wet basis 7.20 Carbon % dry basis 68.77 Hydrogen % dry basis 4.55 Nitrogen % dry basis 1.27 Oxygen % dry basis 12.08 Sulfur % dry basis 0.45 Ashes % dry basis 12.87 High heat value (dry basis) KJ/kg 25,911 Lower heat value (wet basis) KJ/kg 23,155

**Case As generated Separated** Water content % wet basis 45.58 24.93 Carbon % dry basis 42.70 38.50 Hydrogen % dry basis 5.93 5.35 Oxygen % dry basis 37.95 34.22 Ashes % dry basis 13.42 21.93 High heat value (dry basis) KJ/kg 16,244 14,647 Lower heat value (wet basis) KJ/kg 8,129 10,111

There is no general rule to assure success of a MSW gasification or co-gasification facility; it depends on the technology used, the nature and variability of the feedstock, and strongly on the local cost and price structure. Where landfilling is still cheap and permitted, WtE tends to be not an economically feasible option. But where waste disposal is becoming more regulated and costly, a WtE plant of this kind is a great option to reduce the amount of material disposed and its inertness while having a benefit, that could be the obtention of energy or of value-added

## *Waste to Energy and Syngas DOI: http://dx.doi.org/10.5772/intechopen.85848*

*Sustainable Alternative Syngas Fuel*

Canada [18]. Mitsubishi Heavy Industries has a medium-sized plant in Kushiro, Japan, which has been operating since 2006, processing 240 T/day of MSW

wood to produce syngas to be burned in brick furnaces [24].

• Thermal municipal solid waste gasification [27].

• Thermal processing of waste [28].

of feedstock and technology [29].

(2 units × 120 T/day), producing 4.6 MW of electricity. Their technology includes an ash melting system that improves the ash quality and controls the dioxin emissions [19]. Currently, Fulcrum-Bioenergy is preparing the construction of a MSW gasification facility in Nevada (USA) to produce 10 million gallons a year of biofuels [20]. Aries Clean Energy has different facilities already working in the USA. In Sanford, Florida, they installed a fluidized bed gasification plant for 30 T/day biosolids from a sewage treatment plant [21]. In Lebanon, Tennessee, a downdraft reactor gasifies 64 T/day of biomass to produce heat that is used with organic Rankine cycles (ORCs) [22]. The same technology was used in Covington, Tennessee, with a reactor of 12 T/day mixture of wood residues and sludge moving a 235-kW ORC [23]. In Boral Bricks, Alabama, 12 modular downdraft systems were used to process residual

Tanigaki et al. have reviewed the operation of two plants in Japan. They reported more than 46 gasification facilities working nowadays in Japan but focused on the two more recent ones, one processes MSW with higher operating hours and lower consumables in Japan. The other one is focused on its waste flexibility, processing not only MSW but also IBA, rejects from recycling center, and sewage sludge. They show the reliability of these plants as well as their effectiveness on the MSW treatment, energy efficiency, and accomplishing environmental requirements [25].

There are many gasification facilities in the world. A good review of them can be found in the Worldwide Syngas database of the Global Syngas Technology Council [26]; here, the facilities can be located and filtered by feedstock, product, and technology among others. In the following studies, in addition to very good technological reviews of the MSW thermal treatment, especially on gasification, there are sets and lists of plants, facilities around the world with their capacities and owners.

• Municipal solid waste (MSW) to liquid fuels synthesis, volume 1: Availability

• Gasification of non-recycled plastics from municipal solid waste in the United

There can be found good examples of feasible and working projects for MSW treatment; however, it is important to note that these projects have specific and contextual difficulties. Hakan Rylander, an experienced actor in WtE, is a bit skeptical about gasification of MSW, mostly because of the heterogeneity of the feedstock, and because the energy balance sometimes has turned out to be negative [33]. Also, Tangri and Wilson [34], make an interesting risk analysis of the gasification and pyrolysis of MSW. They conclude that "the potential returns on waste gasification are smaller and more uncertain, and the risks much higher, than proponents claim," "Technical and economic challenges for gasification projects include failing to meet projected energy generation, revenue generation, and emission targets. Gasification plants also have historically sought public subsidies to be profitable." At the end of

• Feasibility study on solid waste to energy: Technological aspects [30].

• Thermal plasma gasification of municipal solid waste (MSW) [32].

States: Thermal municipal solid waste gasification [31].

**6**

the document, there is a list of ten notable cases of plants and facilities around the world that have stopped operations.

There is no general rule to assure success of a MSW gasification or co-gasification facility; it depends on the technology used, the nature and variability of the feedstock, and strongly on the local cost and price structure. Where landfilling is still cheap and permitted, WtE tends to be not an economically feasible option. But where waste disposal is becoming more regulated and costly, a WtE plant of this kind is a great option to reduce the amount of material disposed and its inertness while having a benefit, that could be the obtention of energy or of value-added chemicals.
