Journal

MSW Gasification Carillo, Mationg, Penuela, Rosas Page 1 of 24

SYNTHESIS GAS CONVERSION OF METRO MANILA MUNICIPAL SOLID WASTE THROUGH GASIFICATION

FOR 5MW GAS TURBINE ELECTRICAL ENERGY PRODUCTION

Carillo, Renz Roe, Mationg Hansel Paul, Penuela

Jasmine Helden Therese Rosas, Leo Angelo

Advisers: Jay R T. Adolacion

Dr. Rizalinda L. de Leon

Department of Chemical Engineering, College of Engineering University of the Philippines, Diliman, Quezon, Philippines

Received and Accepted on April 5, 2011

Abstract Turning trash into money is both an economic and environmental dream. But this dream has already been slowly realized in Europe and in some parts of Asia through the chemical engineering process of Gasification. This process not only converts coal and biomass into useful Synthetic Gas (SynGas) but also handles Municipal Solid Wastes (MSW). This paper showcases the conceptual and technical design of a gasification and energy plant that converts MSW from Metro Manila into usable five Megawatts (5 MW) of electric energy. The plant design is divided into four parts which corresponds to four major areas of the plant. The first area manages the gathering and pre-treatment of raw MSW taken from Tanza, Navotas dumpsite. The second part involves the gasification of MSW into syngas and the third part administers the post treatment of the gas. Lastly, after post treatment, the syngas is fed into a gas turbine generator which constitutes the fourth area of the plant. All major equipment comprising the plant has in-depth technical specifications and analyses with information gathered from numerous literatures. In addition to the technical aspects, the paper includes a market study and economic breakdown of the plant in order to determine its feasibility once in operation.

Keywords: Municipal Solid Waste, Gasification, Synthetic Gas, Gas Turbine Generator, Waste to Energy

I. Introduction

The proposed plant aims to generate electricity from synthetic gas, which will be produced from the gasification of

municipal solid waste. The goal is to develop an economically viable process in generating power by producing industrial grade synthetic gas from municipal solid waste. It is desired that


overall, the plant may not only be a profitable business venture, but serve as an environmentally friendly waste disposal method for municipal solid waste as well.

The Philippine electrical power industry is also analysed, so as to determine the potential of the industry in the market in the country. Based on economic data from the previous years, the demand for electrical power is continually increasing through time, majority of which are used for residential, industrial and commercial purposes.

The economics of synthetic gas as source for the electrical power is also analysed based on the national data for natural gas. It was also found out that the main usage for natural gas in the Philippines was for power, which is in line with the objectives of the proposed plant.

The processes and equipment involved are divided into four stages namely the (1) pre-treatment of municipal solid waste, (2) gasification of municipal solid waste to synthetic gas, (3) cleaning of synthetic gas, and (4) generation of electrical energy from synthetic gas produced. There are a total of 11 processes used, majority of which will be used for the pre-treatment, gasification and cleaning. The processes and their corresponding equipment are discussed in more detail, inclusive of the properties, calculations, optimization and hazards of each.

II. Market Study

a. The Design Problem

As the world becomes more technologically advanced, more and more innovations and inventions are being developed. Most, if not all, of

these innovations require electrical energy in order to function, thus, increasing the demand for energy worldwide. In the Philippines, the demand for power is increasing with 20,000 Gigawatt-hour (GWh) in just a span of 9 years. Currently, the major sources of energy in the country are the hydroelectric power and natural gas and coal combustion. (Department of Energy, 2009) This reliance on fossil fuels is a huge disadvantage to our country economically and environmentally. As more fossil fuels are being burned, more carbon (and greenhouse gases as well) is released to the atmosphere, causing harmful effects to both health and the environment. Also, most of the world‟s oil reserves are monopolized by the Organization of Petroleum Exporting Countries (OPEC), which is highly unfavorable for the other OPEC-dependent countries as political and economic instability greatly affect the dynamics of the industry.

Aside from our growing energy needs, another problem faced by our country is the disposal of municipal solid waste (MSW). Municipal solid waste (MSW) refers to all non-hazardous solid waste that includes household garbage, refuse (metal scrap, empty containers), sludge from wastewater treatment plants, and other discarded materials. Here in the Philippines, the most common form of MSW disposal is through landfilling. Landfilling is considered a negative-income activity since it consumes large areas of land but fails to generate revenues. Currently, controlled dumps in the outskirts of Metro Manila are responsible for the disposal of all of Metro Manila‟s MSW. The passing of The Ecological Solid Waste


Management Act (RA 9003) in 2001 has already provided the legal framework for the establishment of a systematic and ecological solid waste management (SWM) program. RA 9003 also allows the awarding of incentives to institutions that undertake effective SWM programs. Despite the passing of R.A. 9003, there is still an impending garbage crisis in Metro Manila with the continuing increase in MSW generation per capita, along with the increase of population in the area. A study done by Navarro in 2003 shows that the current SWM sector will not be able to sustain itself with the escalating prices of SWM. (Navarro, 2003).

With this, we can see that there is a great need for a sustainable and profitable MSW disposal system as well as an alternative power generation setup.

This study aims to develop an economically viable process for the production of 5 MW of power from municipal solid waste as a profitable business venture and to serve as an environmentally friendly waste disposal method. Specifically, the study seeks to:

•Design, simulate and optimize all the equipments necessary in the generation of electricity from syngas made from MSW

•Provide an overview on the current landscape of the energy industry

•Analyze hazards and risks involved in the equipments and processes

•Provide the piping layout and PID of the power plant

•Explore the economic feasibility of MSW gasification and power production

•Provide sensitivity analysis and project profitability of the proposed plant

b. Energy Demand

Electric power has great global demand as technological advancements cause more and more devices to be invented and manufactured. Most of these devices are usually run by electrical energy – whether stored in batteries, or transferred from electrical sockets. With the continuous industrialization of our country, our reliance of electric energy has increased. As seen in the figure below, the demand for power increases along with time, with the power consumption increased by around 20,000 Gigawatt-hour (GWh) in a span of 9 years, where 1 watt is 1 joule of energy per second. The data below consists of the power consumption for the past 9 years, with imports added and exports subtracted.

Figure 1. Power Consumption

As seen in the figure above, the energy consumption for the Philippines has been projected to have an increasing trend. For the span of time considered in the graph, Philippines has been consistently at the top 45 countries in electric consumption worldwide, three


of which are topped by United States of America, China and Japan, respectively. Furthermore, electric production in the Philippines for 2011 was estimated in 2009 to be 61, 9930 GWh the electric consumption to be around 54400 GWh. Imports and exports are still non-existent for the Philippine industry (IndexMundi, 2010).

c. Metro Manila Municipal Solid Waste

One major advantage of this proposed project is the raw material at which the production of electricity will come from. Disposal of Municipal Solid Waste through landfill is in itself a resource spending activity and thus provides no positive financial gain. Additionally, adverse environmental effect of landfilling generates risks that could manifest in several ways such as the „Payatas Tragedy‟ in 2000. For those reason, this project would prove to be beneficial in a lot of ways. The accessibility and procurement of the primary raw material in this project is relatively easy and will come at almost no cost. Republic Act 9003, or otherwise known as the Ecological Solid Waste Management Act of 2000, strongly encourages economic activity that would help curtail the problem on Solid Waste Management and Section 45 of the said act provides incentives “to individuals, private organizations and entities, including non-government organizations, that have undertaken outstanding and innovative projects, technologies, processes and techniques or activities in re-use, recycling and reduction” of Solid Waste. Thus, the cost of obtaining MSW would either be small and negligible or it could even be a revenue generating activity if coordination with the National Solid

Waste Management Commission can be made and approved. However, a major downside on the use of MSW as a biomass feed for gasification is its heterogeneity. Solid Waste could come from a very wide range of sources and thus the components present in the feed could not be easily controlled. For this reason, an elaborate pre-treatment must be done accordingly to produce a more uniform and homogeneous feed. Designing the pre-treatment process would require strategies at which the particle sizes of the feed that would be entering the main reaction phase are consistent and the relative composition is more or less steady. Furthermore, removal of unwanted components (i.e. non-hydrocarbon wastes) should be employed in the design of the pre-treatment process. The design of post-treatment processes will also heavily rely on the specifics and requirements of the gas turbine that will be used to produce the electricity. Aside from the MSW, one other major raw material for this process is the catalyst that is to be used in the gasification stage. To further minimize production costs, air will be the preferred material to be used. Again, this raw material will come at a very little or almost no cost. Procurement of this raw material therefore is not a major problem. The target amount of solid waste to be processed every day will be 100 metric tons. This will be the targeted amount since most of the existing MSW gasifiers in larger cities around the world process around 150 to 400 tons of MSW per day.

d. Target Market and

Competition The electricity generated by the

proposed plant will be the distributors for electric power, which are part of the


second sector of the electric power industry in the Philippines. The current largest distributor of electricity in Metro Manila is Manila Electric Company (Meralco), which is among the top 5 largest companies in the country. It is, however, the only distributor of electric power in Metro Manila, dispensing electrical energy to about 31 cities and 80 municipalities in the region (Meralco, 2009).

Possible competition will be existing companies like National Power Corporation (Napocor) and the First Philippine Holdings Corporation (First Holdings), which also produce power and sell to electric power distributors such as Meralco. According to the Computation of Generation Charge document (2010) of Meralco, the other power sources they distribute for are Wholesale Electricity Spot Market (WESM), Philippine Power Development Corporation (Philpodeco), Montalban Methane Power Corporation (MMPC), and other Independent Power Producers (IPP) such as Quality Power Products, Sta. Rita Gas Turbine Power Plant, and San Lorenzo Combined Cycle Gas Turbine (CCGT) Power Plant. The energy share of these sources is presented as a pie graph in the figure below.

Figure 2 Energy Share

Sta. Rita and Napocor (NPC) are the largest sources of electric power of Meralco, as seen in the figure above. Sta. Rita is a combined-cycle natural gas power plant in Batangas owned by First Gas Power Corporation which is a division of First Holdings. The plant produces 1,000 MW of power (First Gas Power Corporation, 2010). Similar to Sta. Rita is San Lorenzo CCGT which supplies 500MW power and has 13.06% market share (San Lorenzo CCGT Power Plant, Batangas City, Philippines, 2010).

Napocor, on the other hand, generates its own electricity, but the same time also buys electricity from Independent Power Producers (IPPs). NPC used to have monopoly over power generation, until the generation sector of the industry was opened to private investors by the effectivity of Executive Order No. 215 (DOE, 2005).

The smallest sources are Philpodeco and MMPC. Philpodeco is a power company that owns three mini-hydroelectric plants located in the Laguna areas (Miras, JC, 2006). The plants generate a sum of less than 2MW of power. On the other hand, MMPC is a methane converting power plant that derives energy from the Montalban Landfill. The plant is projected to produce 8.19MW of power but only a “very small level” is currently being used due to technical problems (Añonuevo, 2009).

Existing power plants in Manila are Duracom Unit 1 &2 and East Asia Diesel, both diesel plants found in Navotas, Philippines (DOE, 2006).

Based on the available data, the proposed Gasification plant with 5.19MW output and operates continuously, shall have a market share of about 0.153%.


e. Plant Location Electricity in Metro Manila is

generated by National Power Corporation (Napocor), a government-owned and controlled corporation (GOCC). It is currently ranked third among 20 largest companies in the Philippines, “legislated into existence” by Commonwealth Act No. 120 on 1936 (Fay, 2010).

Independent power generators in Luzon contribute to the total power generation as well. Electricity is transmitted using high tension wires by the National Grid Corporation of the Philippines (NGPC), which is owned by private investors, and distributed by the Manila Electric Company (Meralco), the only company allowed for electric distribution (DOE, 2005).

The plant will be located in Tanza, Navotas, Metro Manila. The raw material for the proposed power plant is municipal solid waste (MSW). It will, thus, be physically and financially strategic to have the plant located within the immediate area of a dumpsite. This will ensure less cost for transportation of raw materials, ergo, maximizing the profit. Compared to the Payatas in Quezon City, the location of another dump site in Metro Manila, Navotas is dense (more buildings per land area) and has low coastal area, making it prone to calamities, especially of storms.

As of year 2000, a total of 49,450 exist in different barangays in Navotas, around 8.49% of which are found in Tanza, where the dumpsite is more specifically located. As of December 2010, 39.67 hectares is converted into land fill, which is 3.71% of the total land area (City of Navotas, 2007).

f. Flowsheet Synthesis and Development

In recent years, there have been numerous studies that involve the search for an alternative energy source. This, in large part, is due to the diminishing world supply of fossil fuels. One such alternative that is currently being explored is biomass as an energy source. There are several renewable biomass sources, (i.e. indigenous crops, woods) which makes it an attractive alternative energy source. Hydrogen-rich gas can be produced from biomass after undergoing a process called gasification. Gasification is a process that devolatilizes solid or liquid hydrocarbons, and converts them into a gas with low to medium heating value. The gas produced in gasification can have several applications such as raw materials in various chemical industries or as fuel to power gas turbines. This process will be discussed in further detail later on.

Today, Municipal Solid Waste (MSW) is currently being explored as a biomass feedstock for gasification plants. These studies are aimed to provide knowledge on the utilization of Municipal Solid Waste gasification to serve both as an alternative process for energy recovery and a method for the disposal of Solid Waste. These high temperature energy recovery from MSW are known as Waste-to-Energy (WTE). A more common practice around the world regarding energy recovery from solid waste is the process of combustion. Combustion of solid wastes releases energy as the hydrocarbons reacts completely with oxygen and this energy that is being produced is utilized. However, one major downside of this process is the formation of dioxins/furans (PCDD/PCDFs) in the


flue gas which are proven to be harmful emissions to the environment. Moreover, here in the Philippines, Republic Act 8749, or more commonly known as the Clean Air Act, prohibits the incineration of solid wastes. Therefore, gasification must be pursued since it proves to be the better commercially and environmentally viable alternative. In line with this, our study is aimed at designing a MSW gasification plant that is to be built here in the Philippines, specifically in Metro Manila, one that would help reduce wastes that ultimately end up in dumpsites/landfills, while at the same time the said process would be economically feasible as a commercial venture. This gasification plant will produce synthetic gas (syngas) which is a gas composed mainly of hydrogen (H2) and carbon monoxide (CO). The syngas is then subsequently used as fuel to power a gas turbine that will produce electricity. Market demands for electricity, which was discussed previously, indicates a relatively easy market penetration due to increasing demands in electricity.

III. Process Development

a. Health, Safety, and Environmental Considerations

Gasification is a vital process in the energy industry today, making a promising contribution to the development of renewable energy worldwide. In this light, operational safety and environment compliance should be partnered with this development in the energy industry, as it is currently and will continue to penetrate the energy market, therefore appealing to investors and to common people as well. This can ensure commercialization and improving

promotion for gasification and syngas production.

Dealing with the different risks in health, safety and environment (HSE) is one of the major challenges for new technologies nowadays, usually because of the lack of awareness, knowledge and concern of these issues. Though biomass gasification is already promoted as a better means for renewable energy production, many HSE issues still remain to be addressed. Systematic analysis, study and evaluation of different measures involving health, safety and environment should be carefully done, so as to ensure proper handling and performance for the municipal wastes, the syngas as product and gasification as the major process.

b. Detailed Process

Synthesis Pretreatment

When the feed is delivered to the plant, the pretreatment process begins. MSW, starting at stream 01 is fed into the hammer mill for size reduction. Next, MSW is transferred to a trammel screen for size discrimination. The oversize is assumed to be composed big carton boxes and the like, and shall be directly fed to a rotary shredder. This shall be done manually. On the other hand, the undersize is delivered back to the landfill while the medium size is fed to the conveyor installed with a magnetic head that separates iron from the feed. After iron separation, it is then pass through an eddy current separator which takes out aluminum. The feed then joins the oversize earlier in the shredder. After this second size reduction process, MSW is again discriminated through a vibrating screen. The fines shall enter


the gasifier hopper while the oversize shall go back to the shredder. Gasification

The gasifier hopper temporarily stores the feed and delivers it at a steady rate to the fluidized bed gasifier. The MSW is converted into raw syngas through gasification in the equipment where air serves as the gasification medium. The gasification product composition is discussed in chapter 4 of this report.

Post-treatment and Cleaning

Raw syngas then undergoes post-treatment. It first undergoes catalytic cracking with dolomite which transforms some unconverted product, or tar into more carbon monoxide and hydrogen. The cracker has two columns in order to accommodate dolomite reloading to one of the columns while the other is in operation. Particulates are then removed from the syngas by a candle filter after the cracking process.

Electric Conversion and Heat

Recovery When post-treatment is

accomplished, the syngas is now fed into the gas turbine. The gas turbine converts syngas into electrical energy. The power output of the turbine is 6.42MW. About 1MW of this output is used for the plants energy requirement while the remaining is delivered to electric distribution companies.

c. Mass and Energy

Balance The following paragraphs

describe the material flow in and out of the whole reactor. Several assumptions were made so as to make the calculation straightforward. These

assumptions are based on existing literatures.

The basis for the material balance is a daily operation that would process 100 tons of MSW. This is the basis used by the researchers in calculating all mass and energy balances, in preparing the process flow sheet, in designing equipments, and in calculating the economic feasibility of the proposed power plant

MSW composition is an uncontrolled variable that could widely alter the composition of the produced gas. So for the purpose of this study, the known average compositions of Metro Manila MSW were the basis used for the subsequent computations made, specifically for the pre-treatment process.

Figure 3 shows the Process Flow Diagram of the proposed plant.

IV. Equipment Design a. Pre-treatment

HAMMER MILL

The hammer mill was designed to reduce the particle size of the MSW feed for easier classification in the nest processes. A low-speed, low-torque hammer mill was chosen to avoid explosions caused by undesired components in the feed stream and reduce the wear and tear caused by the feed stream. The particle size of the MSW feed will be reduced from 14.7 cm (average) to -6m (average) in this equipment.

Untreated MSW is composed of different types of materials with different particle sizes. To homogenize the particle size of the MSW, size reduction is necessary. A mechanical crusher, specifically a hammer mill, will be employed to perform the said task. The


Figure 3. Process Flow Diagram


crushing will also reduce the glass

component of the MSW stream to fines,

which will allow easier removal of glass

in the subsequent process. The particles

size distribution of the MSW feed was

assumed to be similar to that of New

York City (Nakamura, Castaldi, &

Themelis)

The MSW feed enters the hammer mill through the hopper to the hammer circle. The rotating hammers in the circle crushes the feed by impacting it. The smaller particle is then allowed to pass through a series off grates where only the material with the appropriate particle size is allowed to pass through. The rejected material is retained in the hammer circle until it is reduced to the desired particle size. (Tchobanoglous & Kreith, 2002) The specifications of the selected hammer mill are shown below.

Parameter Value Unit

Actual Capacity 4.17 ton/hr

Volumetric Capacity 6.683 m3/hr

Rotational Speed 1800 rpm

Hammer length 25.00 cm

Hammer width 6.35 cm

Hammer Thickness 6.40 cm

Selected Hammer Mill Model

MAXI PIG /10

Feed mouth dimension 400x1490 Mm

Power 250 kW(max output)

H 1657 mm

D 1170 mm

W 2612 mm

Table 1. Hammer Mill Design specifications

Figure 4. Hammer Mill

TROMMEL SCREEN

The trommel screen is designed to carry out size discrimination for the crushed MSW. The design allows separation of the feed into three streams: X-3, X-4, and X-5 with particle sizes of -2.54 cm, -6 cm, and +10.12 cm, respectively. The first stream is composed of crushed glass and other undesired fines which will be disposed in landfills. The stream with the largest particles size is assumed to be composed mainly of cardboard boxes and this will be transported to the rotary shredder to be incorporated with the X-7A stream.

After reducing the MSW into smaller particle sizes, the stream must be classified into different streams. The desired particle size for the next processes is -6 cm. Those particles with sizes less than 1 inch are assumed to be glass, which were effectively grinded into fines during the processing in the hammer mill. The oversized components of the feed stream, whose sizes exceed 10 cm, are assumed to be mostly cardboard because they are least likely to be reduced into smaller sizes by the hammer mill. (Tchobanoglous & Kreith, 2002). For the this plant‟s trommel mill, the equipment is expected to completely separate the crushed MSW into 3 streams, whose particle sizes are -2.54 cm, -6 cm, and


+10.12 cm, respectively. To separate the feed stream more effectively, the equipment will be designed with spikes in its interior, which will serve as bag openers for those components trapped in plastic bags. To design the trommel screen for this plant, the efficiency of the equipment was assumed to be 99%, which means complete separation of MSW into the 3 desired streams. Since there is no literature regarding the design of trommel screens, literature values from Tchobanoglous et al and Robinson adopted for this design. The power consumption of the equipment was extrapolated using the empirical data from Caputo et al‟s study. The sizes of the openings for the trommel screen were estimated using the equation below.

Where:

p = probability of the feed particle to pass through the screen d = diameter of the feed particle

a = length of one side of the square opening (or diameter of the circular opening) of the screen

Q = ratio of the area of the openings over the total screen area

Material to be separated is fed into one end of a tubular, rotating screen with a downward slope, so that the material will flow down the screen as it is dropped and tumbled. Blades or prongs are located at the inlet end to open bags. (Tchobanoglous & Kreith, 2002)

Parameter Value Unit

Inclination angle 5 degrees

Diameter 3.5 m

Mesh Size 1 5 cm

Mesh Size 2 8 cm

Screen length 5 m

Rotational Speed 12 rpm

Table 2. Trommel Screen specifications

MAGNETIC SEPARATOR

To remove the ferric components of the MSW feed, a magnetic separator is installed in the pretreatment system. The equipment is expected to remove all the ferric materials, which constitute 4% of the untreated MSW. The removed ferric metal is then sent to a recovery facility for recycling.

The magnetic separator for this process is expected to remove the all the ferric components of the screened MSW. Since the amount of ferric material to be recovered is just a small fraction of the total MSW stream, a magnetic head pulley will be appropriate. This type of magnetic separator is the least expensive and easiest to operate. A permanent magnet was selected to reduce the electric consumption of the plant.

To determine the appropriate size of the magnetic head pulley, empirical data from Perry‟s‟ Chemical Engineering Handbook were used.

The head-pulley magnet will be installed at the end of the conveyor belt. As the MSW stream arrives at the end of the conveyor belt, the non-ferric material falls off the belt while the ferric waste is attracted to the head pulley and is retained on the belt. Once the attracted material passes through the bottom of the belt, it falls off as soon as it is moved away from the magnetic pulley. The ferric materials separated will be collected and transported to a


recycling facility. The computed specifications for the magnetic head pulley are shown below.

Selected Pulley diameter

mm 914

Belt velocity m/s 1.855

Belt width mm 457

Maximum depth of material (Table 19-18, Perry's)

Mm 191

Table 3. Magnetic Separator specifications

The head-pulley magnet is

installed as an integral part of the belt conveyor. As material falls off the end of the conveyor, the head-pulley magnetic forces hold magnetic material to the belt, attracting the magnetic materials and changing their trajectory as they fall off the end of the belt. Under burden material, which is entrapped under the magnetic metal, will be held onto the belt by the magnetic material above it and carried over into the magnetic product, resulting in contamination. EDDY CURRENT SEPARATOR

The eddy current separator serves as a separator for non-ferric metal waste from the MSW stream. For this process, all non-ferric metal waste is assumed to be aluminum. The aluminum waste will be collected and sent to a recycle facility.

This process must remove all the metal waste which was not removed from the previous process, which is assumed to be aluminum. Aluminum waste comprises 1% of the total MSW feed. An eddy separator is appropriate for this process since it allows easy separation of aluminum from MSW. To determine the appropriate specifications for the said equipment, a selection table from Eriez Magnetics Europe Ltd was used.

The eddy current separator produces a magnetic field that induces an electric current in metallic components of the MSW feed. The induced electric current then generates a secondary magnetic field, which is opposite to that of the primary magnetic field. This causes a physical repulsion of the metallic waste from the main stream. Due to the low conductivity and density of aluminum, it is easily repelled and separated by the equipment. Based on the type of MSW feed and inlet flow rate, the following specifications were determined.

ECS Model LC

Magnetic Scalper CP and pulley

Actual Capacity ton/day 83

ton/hr 3.458

Capacity per 1000mm Feed width (Shredded refuse, 50-150mm)

ton/hr 20

Minimum feed width

mm 172.9

Separator Dimensions/Type

ECS Model 12

Weight kg 450

Total Power 6.25

Feed Width A 305

Distance bet. Pulleys

B 1500

length (w.out hopper)

C1 2110

width E 899

System height G 1840

System Length H 4120

Table 4. Eddy current separator specifications

ROTARY SHEAR SHREDDER


After removing the unwanted components of the MSW feed, the stream must be further homogenized and its particle size must be reduced to less than 6 mm before entering the fluidized bed gasifier. The rotary shear shredder will allow size reduction of streams X-8 and X-9, whose average particle sizes are -6 cm and +10 cm.

In order to achieve the required particle size for the fluidized bed gasifier, a more uniform size reduction process must be added to the pretreatment process. A rotary shredder is the most appropriate since it is able to cut the paper and plastic components of the MSW into shreds effectively. The inlet MSW stream into this equipment is assumed to be of uniform size, with particles finer than 6 cm. The desired particle size is less than 6 mm, which is the maximum allowable particle size for the fluidized bed gasifier.

To compute for the appropriate design for the rotary shear shredder, the density and volumetric flow rate of the inlet stream were determined. The particle size distribution of the resulting product from the shredder were adopted from the empirical data from Tchobanoglous et al.

The rotary shear shredder is essentially a continuous rotary shear or scissor. Material is fed into counter rotating shafts with closely spaced cutters. This type of shredder tends to cut feed material into strips, which are the same dimension as the cutter width or spacing. The cutters are not circular, but rather oblong. Material passes down through openings that form between the tops of opposing cutters from opposite shafts. Hooks are positioned on each cutter to grab material that enters the mill and pull it into the shear where it is cut. (Tchobanoglous & Kreith, 2002)

The specifications of the chosen shear shredder are shown below. (Shredders & Grinders - TWIN SHAFT SHEAR TYPE)

Model HT80-3526

Motor Power 2 x 40 HP

Feed Size L x W 35" X 26"

Shaft Distance 12

Rotor Thickness 1.2" / 2"

Rotor Diameter 13.6"

Rotor Speed -rpm 22 / 20

Machine Weight 7700 lbs

Table 5. Shear shredder specification

VIBRATING SCREEN

The vibrating screen allows removal of particles with sizes greater than 6 mm from the MSW stream. The oversize is sent back to the rotary shear shredder where it is reduced to the desired particle size.

To separate the fraction of the MSW stream with the desired particle size, a separator equipment is needed. For this function, a vibrating screen is the most appropriate equipment due to its high efficiency. The oversize stream is returned to the rotary shear shredder to reduce it to an admissible size while the undersize is transported to the storage silo for gasification.

Vibratory screens are flat screens mounted at an angle, which facilitates material movement. During operation, the screens vibrate up and down to allow undersize particles to pass through it. (Tchobanoglous & Kreith, 2002). The acquired specifications of the screen is shown below, as collected from the Shanghai Shibang Machinery Catalogue. (SHANGHAI SHIBANG MACHINERY CO., LTD.)


Type

YA1237

Screen Spec mm 1200x3700

Layers

1

Sieve Pore mm 3-50

Max Feed Size mm 200

Capacity t/h 7.5-70

Power kW 5.5

Vibrating Frequency

Hz 800-970

Incline of Screen degrees 5

Table 6. Vibrating screen specification

b. Gasification

FLUIDIZED BED GASIFIER

The design of a MSW fluidized bed gasifier was performed which required the desired energy from the gas turbine and ultimate analysis of the MSW feed. The ultimate analysis was approximated by utilizing the Metro Manila average compositions and an older ultimate analysis study of MSW from USA. The sizing and streams of the gasifier were obtained by an established process calculation. On the other hand, the composition of the product was estimated by using a stoichiometric model. Lastly, the controls for a gasifier and its corresponding HAZOP were presented. The heart of the energy conversion plant is the gasification stage. This is where the pretreated MSW is converted into usable Synthesis Gas (Syngas). Gasification is basically heating with the presence of less stoichiometric air requirement. This prevents complete combustion from happening which is undesired since this turns the feed into unusable products instead. The basic compositions of syngas are Carbon Monoxide and Hydrogen gases with some amounts of Carbon Dioxide and Nitrogen.

Gasification of Municipal Solid Waste (MSW) is somehow complicated due to its properties. Its kinetics has not been studies extensively compared to coal gasification. Yet it is possible to design a MSW gasifier by considering the feed as a form of biomass and obtaining the ultimate analysis composition of the MSW feed. Several papers have been published that shows how gasifier design-specifications can be calculated using ultimate analysis data of any feed.

Desired Product Gas Power Output

MWth 20.1771429

Desired LHV of Product Gas

MJ/Nm3 4.75

Biomass/Fuel LHV MJ/kg 22.1812788

Gasifier efficiency 0.89 Air Equivalence Ratio

ER 0.2654979

Stoichiometric amount of air required

kg/kg dry fuel

7.34104838

Fluidization Velocity

m/s 35.4172849

Maximum Volumetric biomass capacity of gasifier

kg/m3.h 1120

Product Gas Flow Rate

Nm3/s 4.2478195

Biomass/Fuel Feed Rate

kg/s 1.0220757

Air Flow Rate kg/s 0.0191727 Cross Sectional Area

m2 0.4618645

Volumetric Air Flow Rate @ 875 C

m3/s 0.0630913

Minimum Bed height

m 7.1130023

Diameter of gasifier

m 0.7668534

Table 7. Gasifier specification


c. Post treatment

CATALYTIC TAR CRACKING Catalytic tar cracking is the first in

the series of gas clean up processes. This process is done to reduce tar concentration on the synthesis gas produced from the gasification process. Tar is a complex mixture of condensable hydrocarbons, including, among others, oxygen-containing, 1- to 5-ring aromatic, and complex polyaromatic hydrocarbons (L. Devi et al., 2003). For Gas Turbine applications, tar concentrations of the synthesis gas must be reduced to a tolerable level that the turbine can withstand and accommodate.

For our process, dolomite will be used as the catalyst. Dolomite is a cheap, non-metallic, disposable catalyst that performs well in reducing tar concentration of gasification product gas.

One of the main obstacles faced by biomass gasification technologies is the presence of considerable amount of tar and particulate matter in the synthesis gas produced from the process. The typical level of tar concentration for fluidized bed biomass gasifier is 10 g/Nm3. Tar is considered to be an undesirable by-product of the gasification process due to some potential problems that it could cause. Examples of these nuisances are (L. Devi et.al, 2005):

•Condensation and subsequent plugging of downstream equipment •Formation of tar aerosols •Polymerization into more complex structures Therefore, reducing the tar

concentration of the product gas is a

vital step in the utilization of the synthesis gas for power production. Specifically for gas turbine use, the limit for biomass gas tar concentration is within the range of 0.05 to 5 g/Nm3. In order to attain this required concentration in our process, catalytic decomposition of the biomass tar is to be done in a reactor, using dolomite as the catalyst.

The process undergoes heterogeneous catalytic reaction. Using the rate constants calculated from the study by L. Devi et.al, a reactor will be designed assuming plug flow conditions, and utilizing the calculated apparent rate constant and activation energy determined from the experiment in formulating a global rate expression for the reaction.

From the study mentioned above, several considerations were made such as plug flow conditions. The apparent value of the constants that were determined already accounts for the effect on overall rate of transport (bulk to interface and intraparticle) and adsorption/desorption. Likewise, first order reaction mechanism were assumed for the global rate of the reaction.

From the apparent reaction kinetics constants, the space time, catalyst amount, and catalyst-sand mixture amount were calculated.

The reactor design for the lab scale reactor used in the study will be the basis for the industrial scale design. After performing the calculations, the results indicate the need for approximately 266 kg of dolomite or 1.2 tons of the catalyst-sand mixture per reactor. Two 12 L stainless steel fixed bed reactor (1 m diameter, 15 m height) will be used. These results are all based on and in line with the study by L. Devi


et.al, thus the design method is highly dependent on the said study. The table below summarizes the result of the calculations.

K0,app (m3/kg h) 7.2 x 1010

E (kJ/mol) 196 R (J/mol K) 8.314 T (K) 1073.15 e-Eapp/RT 2.88089 x 10-10 K (1/s) = K0,app x e-E/RT 20.74239642 Conversion Desired 95% Space time (kgcat h/m3) 0.144425563 Flowrate (m3/h) 1845 Amount of catalyst (kg) 266.4651631 Amount of mixture (kg) 1567.442136 Table 8. Tar Cracker calculations

CANDLE FILTER

Following the initial gas clean up step that reduces the tar concentration through catalytic reaction with dolomite of the tar present in the produced synthesis gas, the removal of dry solid particulates will be done through candle barrier filters. Candle filters are porous, ceramic, or metallic. (Basu, 2010) The porosity will depend on the size of the finest particles that must not be allowed to pass through. These particles will then deposit on the wall and form a layer of solids called a “filter cake.”

The candle filter design will be determined based on the results of the study indicated on the report by T. Lippert et.al for Westinghouse Advanced Particle Filter System. The specifications of the filter will be based on the results of the biomass hot gas filter tests conducted.

Gas Flow 1000 to 1700 ACFM

Filter Pressure

1.4 to 2.4 Mpa (200 to 350 psig)

Filter Gas Temperature

1200 to 1900°F

No. of Candle Elements

64

Face Velocity 2.9 cm/s (5.8 ft/min)

Inlet Dust Loading

18,400 ppm

Outlet Dust Loading

Not Detectable

Table 9. Candle Filter specifications

The result of the equipment

design indicates the requirement for a Hot Gas Filtering Refractory Lined Vessel diameter of 10 ft., with 64 candle elements that are 1.5 m long. This design for the gas filtering is enough to reduce the biomass gas particulate in the synthesis gas to allowable limits. This design method depends largely on the reported performance of the SPPC Pinon Pine Hot Gas Filter in the tests conducted.

d. Gas Turbine

GAS TURBINE The second most important component of the plant is the gas turbine package which converts post-treated syngas into energy. The design of the turbine is simple since selection of a packaged product was done beforehand. The second key component of the waste-to-energy plant is the conversion of syngas to mechanical and electrical energy by a gas turbine. The gas turbine design process is simple since the proponents have established a specific gas turbine package. The specific package is the Allison (Rolls-Royce) 501-KH5 Gas Turbine Package which is currently available in the market.

Figure 4 shows the Gas Turbine equipment specification by a) manufacturer and b) package dealer.


Figure 4a. Gas Turbine manufacturer specification

Figure 4b. Gas Turbine Package dealer specifications

In addition to the information stated above, syngas flow rate and energy demand was sought. After the calculation process, the proponents obtained the syngas flow rate and process energy demand to be at 3.3928 Nm3/s and 20.1771 MWth.

V. Economic Analysis a. Cost Estimation

The first major factor considered

in this chapter is the Total Capital Investment. This is the amount in which the plant needs in order for it built. The capital investment basically comprises the total cost of equipment purchase and the site development. The second major factor considered is the Total Product Cost. This is the amount needed to produce one unit of product.


To complete the feasibility study, all the costs shall be compared to how much the plant will gain in revenue. Engineering Economics methods such as Present Worth and IRR analysis shall be done to effectively determine if the proposal is an attractive venture or not. Sensitivity analysis is also presented in the later part to determine which factors of cost greatly affect the plant‟s desirability.

We begin the calculation of TCI by determining how much all in all the equipment are worth. The prices of each of the equipment discussed in the Mass and Energy Balance Chapter were already mentioned. Next, the other factors for TCI were estimated using Table 17 of Peters and Timmerhaus (1991). Assigning the total purchased equipment as 100 over 487, the total capital investment can now be easily determined. Using the total PhP 369 M, the total capital investment is calculated by multiplying the amount to 487 over 100.

Equipment Equipment Cost (PhP)

Hammer Mill 13,156,209.99 Trommel Screen 4,252,085.81

Magnetic Separator 2,646,283.38

Eddy Current Separator

529,256.68

Rotary Shredder 3,804,328.78

Vibrating Screen 180,443.35

Vibrating Bottom - Silo

1,020,381.33

Centrifugal Air Compressor

2,583,554.68

Gas Turbine 43,830,813.10

Fluidized Bed Gasifier 233,081,114.43

Pyrolysis 0.00

Candle Filter 45,101,906.68

Air Preheater Furnace (for Gasifier)

5,783,826.44

Conveyor Belt 2,660,530.36

Feed Conveyor 1,375,234.19

Tar Reactor 956,958.14

Table 10. Summary of equipment cost

Amount (PhP)

%

Purchased Equipment (Delivered E.C.)

369,417,439.69

20.53

Installation 144,072,801.

48 8.01

Instrumentation and Controls

48,024,267.16

2.67

Piping 114,519,406.

30 6.37

Electrical 36,941,743.9

7 2.05

Buildings and Services

107,131,057.51

5.95

Yard Improvements

36,941,743.97

2.05

Service Facilities 203,179,591.

83 11.29

Land 22,165,046.3

8 1.23

Engineering and Supervision

118,213,580.70

6.57

Construction Expense

125,601,929.49

6.98

Contractor's Fee 66,495,139.1

4 3.70

Contingency 132,990,278.

29 7.39

Working Capital 273,368,905.

37 15.20

Total Capital Investment

1,799,062,931.27

100.00

Fixed Capital Investment

1,525,694,025.90

85.00

Table 11. Breakdown of total capital investment


% of Fixed Capital Investment

PhP/year Notes: % from Taxable Product Cost

Raw Materials 0.00% 0.00 Raw material is MSW. It is assumed that the plant will obtain MSW with no cost.

0.00%

Operating Labor 0.08% 1,169,671.35 See Operating and Other Labor Cost Calculations

0.72%

Direct Supervisory and clerical labor

0.02% 303,828.55 See Operating and Other Labor Cost Calculations

0.19%

Utilities 0.34% 5,212,892.76 Natural Gas and Dolomite. See Utilities Tab for NG and Dolomite.

3.19%

Maintenance and Repairs

4.44% 67,808,623.37 See Maintenance and Repairs Cost Calculations

41.54%

Operating Supplies

0.67% 10,171,293.51 Assumed 15% of Maintenance and Repairs Cost

6.23%

Laboratory Charges

0.01% 175,450.70 Assumed 15% of Operating Labor Cost

0.11%

Patents and Royalties

0.28% 4,258,811.77 0 to 6% of Product Cost 2.61%

Depreciation 3.84% 58,614,233.76 Used Straight Line Method of Depreciation based on MACRS-GDS Recovery Period

35.90%

Local Taxes

Insurance 1.00% 15,256,940.26 Assumed 1% of Fixed capital investment.

9.35%

Rent 0.00% 0.00 Assumed land shall be bought and no buildings shall be rented.

0.00%

Plant Overhead Costs

2.72% 41,569,273.96 Assumed 60% of Labor, and Maintenance and Repairs Costs

25.46%

Administrative costs

0.02% 292,417.84 Assumed 25% of Operating Labor Cost

0.18%

Distribution and selling costs

0.19% 2,839,207.85 2 to 20% of product. (2%) 1.74%

Research and development costs

0.93% 14,196,039.23 2 to 20% of product. (15%) 8.70%

Total Product Cost

163,254,451.14 Without Depreciation

104,640,217.38 With Depreciation

Table 12. Total Product Cost Breakdown


Total Product Cost As mentioned in the Mass and

Energy Balance chapter, the cost of obtaining raw materials is zero since it was assumed that the operators will acquire MSW for free. This scenario may be possible since it would be beneficial to local authorities if the problem of MSW is shared by another company or group.

The Cost of Operating Labor was achieved by assigning appropriate laborers for each process stage or machine involved in the plant. In addition, control and chemical engineers, and mechanical and electrical engineers are also assigned to take care of the specific work areas. The wage rate of the laborers for the plant is based on a 2006 survey by the Department of Labor and Employment. The consumable materials that do not count as raw materials are placed as Utilities for the Plant. There are three consumables of the plant that were categorized as Utilities. These are Natural Gas and Dolomite. Since the plant is self-sustaining in energy, electricity consumption is not considered as a utility.

The cost of Maintenance and Repairs was estimated using table 25 of Peters and Timmerhaus (1991) Cost Estimation Chapter. Each operation stage is rated how much wage and material should be allocated for its maintenance and repairs.

The Plant Overhead Cost which also takes care of the electric consumption of the Gas Turbine Generator Station and of the plant such as lights and air-conditioning is assumed to be 70% of the sum of Operating Labor, Supervision and Clerical Labor, and Maintenance and Repairs Costs.

All of the equipment purchased are assumed to depreciate after the effective plant life of 22 years. This plant life is actually stated by the MACRS-GDS depreciation method which is used for this plant proposal. The MACRS states that either Straight Line or Declining Balance with Switch can be used within the recovery period of the plant. The recovery period for a typical power plant is 15 years as instructed by this depreciation method. Straight Line method was used for 15 years. The depreciable materials of the plant other than the equipment include: Instrumentation and Controls, Piping, Electrical, Buildings and Services, and Service Facilities.

The other factors that should be considered for the Total Product Cost such as Insurance, and Research and Development Cost are estimated by giving percentages of various costs already available.

Table 12 provides a breakdown of the total product cost.

Economic Feasibility For one year, the plant shall have

projected gross revenue of about PhP 198 M. This can now be used to assess the plants economic feasibility, including the total capital investment and total product cost. Moreover, dividing the total energy output to the total product cost calculated beforehand, the cost of producing 1 kilowatt-hour of energy is PhP 2.80/kWh. This value is smaller than the selling price of Meralco which indicates that there will be positive revenue for the proposed plant.

The initial revenue should be deducted to the total product cost in order to determine the actual profitability of the plant without any other charges.


But tax laws of the country should be considered too. Taxation should be considered since it will greatly affect the net income of the project. The effective tax rate for a production facility such as this is 35%. Tax is placed on the net income and shall be paid by the future project owners. After this consideration, the final net income is now achieved. The after-tax net income is about PhP 32.83 M.

The payback period is calculated by dividing the total capital investment by the after-tax net revenue per year. The result, which is also in years, is the time it takes for the investment to actually start earning profits and the capital already compensated. The payback period is 29.51 years, which is more than the expected plant life. Hence, this indicates that unfortunately, the plant is not profitable and payback won‟t be attained unless plant is to have a longer life span. Landfill Cost Savings

An international study was made in 1999 by Johannessen and Boyer about the landfill status for most parts of the world. For the Philippines, the Carmona and San Mateo landfills were investigated. They remark that municipalities charged a tipping fee for every truck of garbage delivered to their landfill. For San Mateo, the charge is about USD 1 per 4-wheeled truck delivered or about 10m3 of garbage and USD 1.5 per 6-wheeled truck (15 m3). On the other hand, Carmona landfill charges a flat rate of about USD 5 per truck delivered. There was no direct source of how much it would cost for a landfill but they estimated that per tonne of garbage, the landfill cost is USD 10.

Using this value, we can approximate how much it would cost to throw garbage to a landfill. Using an inflation calculator provided by inflationdata.com, the price USD 10 is currently USD 13.13. And with a foreign exchange rate of PhP 43.83, the cost is 575.71 PhP/tonne.

Even though 100 tonnes/day of MSW is delivered to the site, the actual feed processed is about 90 tonnes/day and the rest gets delivered back to landfills or recycling facilities. The amount of cost saved by putting up the proposed gasification plant is PhP 15.5 M if the proposed gasification plant is realized. Hence, even if the plant is not profitable in terms of payback years, it is possible to construct the gasification and power plant with the landfill benefit in mind. The revenues saved from the landfill may be used in order to shorten the payback period.

VI. Conclusion and Recommendations

The report proposes a municipal solid waste (MSW) conversion to usable energy. Market study of this report points out the increasing demand of energy in recent years. Synthesis gas was also shown to be increasingly used as power since 1989 at a speedy rate. The current sources of syngas are coal and petroleum. Several competitors have been mentioned in this section including the several natural gas producers in the country. The proposed plant site is in Tanza, Navotas, located near the new landfill area.

Technical discussion of the proposition suggests the utilization of a fluidized bed gasifier, with air as its gasification medium. The process shall produce Synthesis Gas (SynGas) that will be fed in a Gas Turbine Generator.


The whole process is composed of MSW pre-treatment, gasification, post-treatment and cleaning, and electrical energy conversion and heat recovery. A complete process flowsheet and detailed streams were presented. In addition, detailed design process sections for each significant process were also included. The projected power output of the plant is 5.19MW with the amount needed to self-sustain the plant already considered. The report concludes that the proposed method is feasible.

The total capital investment needed for the plant is PhP 1.80B while the total product cost per year is PhP 163M. The net income per year amounts to PhP 60M per year. Economic analysis shows that the plant‟s payback period is 29 years. This is greater than the expected plant life of 22 years. However, considering the savings of decreasing 90 tonnes/day of waste from landfill use, the plant may be economically feasible if the savings are used for the benefit of the plant.


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Journal

Documents

natural gas

energy plant

cleaning of synthetic

gasification of msw

economics of synthetic

nonhazardous solid waste

municipal solid wastes

gas turbine generator