Scholarly article on topic 'Environmental Friendly Ways to Generate Renewable Energy from Municipal Solid Waste'

Environmental Friendly Ways to Generate Renewable Energy from Municipal Solid Waste Academic research paper on "Materials engineering"

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{"Plastic waste" / MSW / gasification / pyrolysis / "fuel ;"}

Abstract of research paper on Materials engineering, author of scientific article — Jaya Rawat, Srinivasulu Kaalva, Vivek Rathore, D.T. Gokak, Sanjay Bhargava

Abstract Economic growth and rapid urbanization are resulting into increase in generation of municipal solid waste (MSW). In India, approximately 68 MT of MSW generated annually in urban areas and more than 80% is disposed in unhygienic manner leading to problems of health and environment to inhabitants. To manage MSW, there is a need to plan infrastructure development. There are many technologies available for handling MSW which treat plastic to convert fuel oil by gasification, pyrolysis, biomethanation and catalytic conversions. The useful products like liquid fuels, chemicals and power are being generated through these processes. The final products need to comply with environmental regulations and demand a lot of technological improvement. Based on MSW/feed quality, there is a need to identify the suitable technology for converting MSW into useful products, which can meet the statuary regulations. Hence, treating MSW, converting into useful products and selection of suitable technology is a big challenge. The present paper focuses to compare: • All suitable treatment technologies and products generated from MSW. • Types of thermal treatments like combustion/incineration, gasification and pyrolysis. It also highlights development of a systematic approach to comply with all environmental regulations to create value for all types of MSW and reduce landfill.

Academic research paper on topic "Environmental Friendly Ways to Generate Renewable Energy from Municipal Solid Waste"

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Procedía Environmental Sciences 35 (2016) 483 - 490

International Conference on Solid Waste Management, 5IconSWM 2015

Environmental Friendly Ways to Generate Renewable Energy from

Municipal Solid Waste

Jaya Rawat*, Srinivasulu Kaalva, Vivek Rathore, D.T. Gokak and Sanjay Bhargava

Bharat Petroleum Corporate R&D Centre, Greater Noida (UP) India

Abstract

Economic growth and rapid urbanization are resulting into increase in generation of municipal solid waste (MSW). In India, approximately 68 MT of MSW generated annually in urban areas and more than 80% is disposed in unhygienic manner leading to problems of health and environment to inhabitants. To manage MSW, there is a need to plan infrastructure development. There are many technologies available for handling MSW which treat plastic to convert fuel oil by gasification, pyrolysis, biomethanation and catalytic conversions. The useful products like liquid fuels, chemicals and power are being generated through these processes.

The final products need to comply with environmental regulations and demand a lot of technological improvement. Based on MSW/feed quality, there is a need to identify the suitable technology for converting MSW into useful products, which can meet the statuary regulations. Hence, treating MSW, converting into useful products and selection of suitable technology is a big challenge.

The present paper focuses to compare:

• All suitable treatment technologies and products generated from MSW.

• Types of thermal treatments like combustion/incineration, gasification and pyrolysis.

It also highlights development of a systematic approach to comply with all environmental regulations to create value for all types of MSW and reduce landfill.

© 2016PublishedbyElsevierB.V. Thisis anopenaccess article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of 5IconSWM 2015

Keywords: Plastic waste, MSW, gasification, pyrolysis, fuel;

* Corresponding author.

E-mail address: jayarawat@bharatpetroleum.in

1878-0296 © 2016 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of 5IconSWM 2015

doi:10.1016/j.proenv.2016.07.032

1.0 Introduction

Increasing global population has led to an increase in the levels of waste produced worldwide. Due to rapid urbanization levels of Municipal Solid Waste (MSW) has increased drastically in last two decades in India. Management MSW is very important from the perspective of public health and the environment. The management of MSW is an organizational, technological and economic challenge. In the hierarchy of objectives, public health is the prime priority. Selection of technology has also to pass the filter of public health responsibility. For sustainability the selected technology should be financial viable. Currently in India two proven means of procedure are being followed for MSW disposal, one is burying MSW in landfills and another one is combusting it in specially designed chambers at high temperatures, thereby reducing it to one tenth of its original volume.

For effective MSW management selection of advanced technologies and methods that helps in keeping our cities clean, prevent pollution and protect the environment and at the same time minimize the cost through recovery of resources and energy. Generation of energy from municipal solid waste in the form of energy or heat either through combustion or production of combustible fuels/ methanol/ethanol or synthetic fuels comes under the category of process defined as waste to energy (WTE).Waste to energy conversion technologies can be employed to convert residual wastes into clean energy, rather than sending the generated waste directly to landfill. There are different technologies to convert solid waste to energy.

2.0 Technologies for MSW Conversions

Selection of appropriate technologies for processing of MSW waste is very much essential; these technologies can be classified into two broad categories namely:

1) Bio-chemical processes

2) Thermo-chemical processes

Bio-chemical conversion of biodegradable MSW covers technologies such as composting and biomethanation, whereas thermal technologies include gasification, pyrolysis, incineration and mass burning. Refuse Derived Fuel (RDF) can also be prepared from combustible MSW and used as a feedstock for WTE plants. Technology for production of syngas also merits consideration (Leena Singh, et al, 2014).

Besides conventional technologies, converting polymeric wastes to liquid fuel called "catalytic conversion of waste plastic to liquid fuel" can also be used for profitably utilizing plastic wastes which are not currently recycled. Figure-1 shows the WTE technologies being adopted worldwide.

2.1 Bio-chemical processes

Bio-chemical processes can be broadly classified in to two categories composting or biomethanation and fermentation.

A. Composting

Composting is an aerobic process in which biologically degradable wastes of MSW are well segregated through a systematic waste segregation process like trommel and magnetic separations, and are converted through solid state biochemical transformation to produce manure/fertilizers or soil nutrients. This is mostly done by two methods:

Fig. 1. WTE technologies

• Vermi composting: In this process, earthworms are used after initial pre-processing of waste under a shed. Here the earthworms eat the organic fraction of waste and excrete - the excreta is collected as vermi casting, sieved and utilized as bio-organic fertilizer. This technology is found suitable for small towns and limited to a class of solid waste where biological portion is high.

• Microbial composting: In this technology, generally large quantities of biodegradable wastes are being handled using windrow method of composting. A lot of new advancements are further being done in this process by selection of good microbes and specialty additives.

Bio -fertilizer or compost is produced by these processes are used in farming and agricultural sector after adding some nutrients.

B. Biomethanation

Biomethanation is an anaerobic process, where solid waste is treated in closed vessels and in absence of oxygen microorganism break down the organic matter and biogas is produced. The biogas produced is used to produce electricity by using gas engines and turbines and the solid residues are utilized as fertilizer. Apart from methane (55-75%), biogas contains significant amounts of carbon dioxide CO2, (30-45%), which is non-combustible, along with smaller quantities and traces of Nitrogen, Oxygen, Hydrogen sulphide, hydrocarbon, Ammonia, water vapour and Siloxanes).

This technology can be conveniently employed in a decentralized manner for biodegradation of segregated organic wet wastes such as wastes from kitchens, canteens, institutions, hotels, and slaughter houses and

vegetables markets. This technology can also be used to manage MSW in a centralized manner in small towns and decentralized manner in large cities provided the municipal authorities collect segregated biodegradable wet wastes from households and establishments. Biogas produced through biomethanation technology can be upgraded into biomethane which can also be used as a transportation fuel. Alternatively, upgraded biomethane can substitute natural gas (a non-renewable fuel) in variety of domestic and industrial applications. Carbon dioxide is typically removed from biogas only when the target is to upgrade it into biomethane.

Comparisons of parameters for bio-chemical conversions of MSW are given in Table-1 as below.

Table 1: Comparison of parameters for bio-chemical conversions of MSW

Parameters Aerobic composting Vermi composting Biomethanation/ Anaerobic digestion

MSW characteristics organic fraction of MSW, organic waste, not much organic fraction only

acidic/alkaline

MSW Particle size Between 25 - 75 mm for optimum Between 25 - 50 mm for optimum Shredded/ pulped particles -

results results increase the surface area for faster

reactions

Moisture content 55% (optimum) 40-55% preferable; sprinkle water as >50%; Implications on feed, gas

required production, system type, system

efficiency

Temperature 50-55 deg C for first few days and 20 - 30 deg C 30-50 with mesophillic and

55-60 deg for the reminder time thermophillic bacteria

pH control 7 - 7.5 (optimum). Not above 8.5 Slightly alkaline state preferable. Slightly acidic to neutral pH range

Area requirement ~25 m2 for 1 ton of MSW Area for Tank size of 4m x 1m x 0.5m for ~25 m2 for 1 tonn of MSW

machinery, packing and storage extra waste input of 10kg/day of semi

decomposed waste

Product Compost approx 18-25% of waste nutrient-rich, natural fertilizer and Biogas; 30% fibres and 50-65%

input soil conditioner fluids

2.2 Thermo-chemicalprocesses

Conversion of MSW through thermal technologies are processes that create energy in the form of electricity, fuel or heat from thermo-chemical processes such as, gasification, pyrolysis incineration or mass burning of municipal solid wastes. MSW after initial pre-processing or segregation is used for these technologies, the details for these processes is described as below:-

A. Incineration or Mass burning

Incineration is mass burning of MSW which results into recovery of heat to produce steam and which can be further utilized to produce power through steam turbines. The complete combustion optimally involves a two-stage transformation of fuel; in this case the combustible material gets converted mainly into CO2 and water vapour. The process also results into generation of lot of toxic dioxins, heavy metal, toxic gases containing chlorides, sulphur and nitrogen along with furans which mostly comes from incomplete combustion of MSW.

This technology is not suitable for aqueous/ high moisture content/ low Calorific Value and chlorinated waste. Excessive moisture and inert content affects net energy recovery; auxiliary fuel support may be required to sustain combustion. Some of the challenges in the acceptability of this technology are noncompliance w.r.t. pollution control norms and meeting emission standards w.r.t. particulate matter and NOx, SOX etc. Although this technique is being used intermittently in India and many other parts of world but still it is not widely accepted due to concern for toxic metals that may concentrate in ash; emission of solid particulate material, SOx, NOx, chlorinated compounds such as HCl and dioxins.

B. Gasification

Gasification is conversion of solid waste biomass/MSW to combustible gas such as hydrogen, synthetic fuels and carbon monoxide, hydrogen and carbon dioxide at elevated temperature (500-1800 deg C). During the process, MSW is segregated in this process to remove non combustible materials. Biomass, agro-residues and RDF (refused derived fuel- comprising of combustible material) pellets can be added to the gasifier to enhance the heat generation. The Syngas is originally for the production of methanol from hydrogen and carbon monoxide, or ammonia from hydrogen. However, syngas, a mixture of hydrogen and carbon monoxide, can be used as a feedstock for further reforming process or can be used as a fuel for production of energy/heat. is also used as gaseous fuel in some facilities for generating electricity. Gasification technology covers not only waste plastics and the other combustibles in municipal wastes but also biomass.

The purpose of gasification of waste is to minimize emissions and to maximize the gain and quality of recyclable products. The process also produces residual waste, as well as waste from cleaning of the gases, which is normally disposed of with a controlled landfill. The Wastewater generated is also normally produced and treated before it is discharged to the sewage system for complying the water specifications as per standard norms.

As compared to incineration, control of atmospheric pollution can be dealt with in a superior way, in techno-economic sense. Gasification at high pressure can further enhance the opportunities to increase energy conversion efficiency and reduce costs. Syngas can be further used, after proper treatment, in gas turbines/engines or can be further converted to chemicals.

C. Pyrolysis

All around the globe companies and individuals are working on technological developments in the area of production of fuel from waste plastic (Industrial and municipal). Compared with developed countries, waste plastic recycle is not significant in developing countries like India. Waste plastic are one of the most promising resources for fuel production because of its high heat of combustion and due to increasing availability in local communities. Their reuse could potentially keep enormous amounts of plastic out of landfills, oceans and rivers.

It is found that every 8 - 15% of garbage by weight is plastic. In terms of volume, the amount of plastic would be 20 - 30% of garbage. Among the plastic waste the most common polymer is low-density polyethylene (LDPE), which is used to make many types of container, medical and laboratory equipment, computer components and plastic bags. In general, the conversion of waste plastic into fuel requires feedstock which is non-hazardous and combustible. In particular each type of waste plastic conversion method has its own suitable feedstock. The composition of the plastics used as feedstock may be very different and some plastic articles might contain undesirable substances (e.g. additives such as flame-retardants containing bromine/antimony compounds or plastics containing nitrogen, halogens, sulfur or nitrogenous or any other hazardous substances), which pose potential risks to humans and to the environment.

Waste plastics are one of the most promising resources for fuel production because of its high heat of combustion and increasing availability in local communities. Total plastic waste generation in India is 36-40 MMTPA, out of which around 60% segregated waste is recycled and rest is disposed by land filling. Recycling initiatives are in place in many parts of the world, but much of the plastic waste ends up in landfill, dispersed in the environment or in the sea. Other few options to explore for usage of waste plastic are use in road making, solid fuels, energy generation, land fill and liquid fuels etc (Yoichi Kodera, 2012).

One of the attractive options for utilizing waste plastics is their conversion into fuel components. The production method for the conversion of plastics to liquid fuel is based on the pyrolysis of the plastics and the condensation of the resulting hydrocarbons. Pyrolysis refers to the thermal decomposition of the matter under an inert gas like nitrogen. For the production process of liquid fuel, the plastics that are suitable for the conversion are introduced into a reactor where they will be decomposed at 350 to 550 °C. Depending on the pyrolysis conditions and the type of plastic used, carbonaceous matter gradually develops as a deposit on the inner surface of the reactor.

After pyrolysis, this deposit should be removed from the reactor in order to maintain the heat conduction efficiency of the reactor. The resulting oil (mixture of liquid hydrocarbons) is continuously distilled once the waste plastics inside the reactor are decomposed enough to evaporate upon reaching the reaction temperature. The evaporated oil is further cracked with a catalyst. The boiling point of the produced oil is controlled by the operating conditions of the reactor, the cracker and the condenser. In some cases, distillation equipment is installed to perform fractional distillation to meet the user's requirements. After the resulting hydrocarbons are distilled from the reactor, some hydrocarbons with high boiling points such as diesel, kerosene and gasoline are condensed in a water-cooled condenser. The liquid hydrocarbons are then collected in a storage tank through a receiver tank. Gaseous hydrocarbons such as methane, ethane, propylene and butanes cannot be condensed and are therefore incinerated in a flare stack. This flare stack is required when the volume of the exhaust gas emitted from the reactor is expected to be large There may be variations in the feeding methods used depending on the characteristics of the waste plastic. The easiest way is to simply introduce the waste plastics into the reactor without any pretreatment.

The main comparisons of parameters for thermal conversion processes of MSW are shown in Table -2.

Table 2: Comparisons of parameters for thermal conversion processes of MSW

Parameters Inceneration Pyrolysis/gasification

MSW characteristics MSW Volatile matter >40%; Fixed carbon <15%; Total Refused derived fuel comprising of plastic/paper wood as

inert <35% combustible material

Calorific value As high as possible; >1200 kcal/kg gross calorific value 3200 Kcal/Kg

Moisture content As minimum as possible; <45% Nil is preferred ( up to 5% can be tolerated)

Temperature not less than 980 deg C in combustion zone 600- 1200 deg C

Residues 3% fly ash (including flue gas residues) 17.3 % (dry basis) , coke

Product 15-25% bottom ash (including clinker, grit, glass), 3% Syngas, electricity/ fuels , plant of 600 TPD Waste

metals capacity can produce Energy of 5 MW. Plastic to oil

plants produce liquid fuels

2.3 Technological Challenges for Plastic -to -Oil

1) Raw material availability, collection and segregation of appropriate plastic: as polyethylene, polypropylene, polystyrene and poly methyl acrylate are more suitable as compared to polymers which contain formaldehyde, polyuretane, polyethylene terephthalate and phenolic resins compounds etc (Nagi Insura, et al, 2010).

2) To adopt same pre-treatment technology for all kind of plastics

3) Yields/Product slates are not in similar range: Non-consistent specifications of products fuel/HSD/MS/Aromatic solvents due to frequent changes in input raw material

4) Product quality details are not readily available

5) Economics of producing BS IV or V level Diesel/gasoline fuel and feasibility

6) NOx, SOx, chlorinated compounds and flue gas generation through some acrylonitrile/PVC type polymers can be a challenge

2.4 Limitations of Waste to Energy production from MSW

• Lack of waste management system adaptability in the social circle and non-awareness of wealth generation from waste.

• Comparable lower energy density of MSW as compared to typical fossil fuels, which is mostly a non-attractive offer for many industrialist to invest into the market.

• The initial capex cost for WTE processes is high, which can only payoff good ROI, if technology supports a lot of concerns on flue gas clean up and waste water treatment along with continuous running of system for longer durations of at-least 3-4 years

[(http://www.energyrecoverycouncil.org/userfiles/file/ASME%20WTE%20White%20Paper%2008.pdf), (Hefa Cheng A et al, 2010)].

• The WTE plants locations should be selected in such a manner so that the waste resources should be closer and cover a bigger domain.

• Incomplete burning of waste can result in the production of noxious gases, such as carbon monoxide and nitrogen oxides. The solution is to strictly control the process with non- allowance of chlorinated plastics/PVCs in the feed.

• The system also requires a hand holding of govt., social, industrial, technology suppliers and NGOs along with funding agencies, where some legal complexities and regulations can also create problems

3.0 Conclusion and Way Forward

• Waste management is a very essential in order to decrease landfill and reduce a lot of environmental and health risks due to unhygienic localities developments.

• Waste-to-energy is a good step to produce renewable energy from MSW/ biomass which can also be helpful in revenue generations.

• Systematic planning of municipal waste collection, segregation and processing them with suitable technologies can help us in development of clean atmosphere with a lot of employment generations in the society at all levels.

• There is a need to educate the public on current thermal/biochemical treatment technologies, and overcome their misconceptions in order to receive their full co-operation in the process.

• The technologies for conversion of MSW to liquid fuel and maintaining their transportation fuel standards are a costly technology and it needs some technological and system improvement. In this context power generation and organic composting can be a good viable and sustainable option for MSW processing, although it requires big capex requirements

• The process for MSW treatment end-to- end scheme to be developed in such a manner so that it should have maximum usage of all parts of waste. The scheme for MSW processing may have following type of processing plan as explained below in Figure-2.

Fig. 2. End-to End MSW processing scheme

Acknowledgements

The authors of this paper sincerely acknowledge thanks to BPCL management for providing their consent and encouragement for presentation of this work.

References

1) Hefa Cheng A, Yuanan Hub, Municipal solid waste (MSW) as a renewable source of energy: Current and future practices in China, Bioresource Technology 101 (2010) 3816-3824

2) Leena Singh, R.Sunderesan, Renu Sarin, Waste to Energy Generation from Municipal Solid Waste in India, International Journal of ChemTech Research, CODEN( USA): IJCRGG ISSN : 0974-4290, Vol.6, No.2, pp 1228-1232, April-June 2014

3) Nagi Insura, Jude Onwudiliand Paul T. Williams, Converting Waste plastic To Gasoline-like Fuel at low temperature, Energy and Resource Research Institute, School of Process, Materials, Environmental Engineering, University of Leeds 2010, http://www.engineering.leeds.ac.uk/dtc-low-carbon-technologies/news-events/2010/documents/waste-plastic.pdf as seen on 20.10.2015

4) Waste-to-Energy: A Renewable Energy Source from Municipal Solid Waste, http://www.energyrecoverycouncil.org/userfiles/file/ASME%20WTE%20White%20Paper%2008.pdf, visited on 20.10.2015.

5) Yoichi Kodera, Plastics Recycling - Technology and Business in Japan, , Book Chapter 10, Environmental Sciences - "Waste Management - An Integrated Vision", book edited by Luis Fernando Marmolejo Rebellon, ISBN 978-953-51-0795-8, Published: October 26, 2012 under CC BY 3.0 license.