“Green is Seen in Fertilizers”

A New Approach to

Municipal Solid Waste Management

By

Carrie Farberow and Kevin Bailey

University of Oklahoma

May 1st

2007

Miguel Bagajewicz

Ch E 4273

1

Executive Summary The production of municipal solid waste (MSW) has steadily increased over the last 45 years from 88 million tons in 1960 to 246 million tons in 2005. Of the waste produced in 2005, about 54% was landfilled, 14% was combusted, and 32% was recovered through recycling or composting. Over the last 18 years, the number of operating landfills has decreased from approximately 8,000 to fewer than 2,000. Due to the decreasing landfill space, especially in densely populated cities, it has become necessary to explore alternative methods for MSW disposal. Pyrolysis, used for municipal solid waste management, has a variety of benefits. The process drastically reduces the mass of waste that must be disposed, remedying current problems related to insufficient landfill space. Additionally, pyrolysis produces synthesis gas which can be further processed to produce a saleable end product, making it more profitable than current incineration facilities. The profitability of a MSW pyrolysis facility is dependent on the end product produced. Several different end products were examined, based on estimates of total capital investment, operating cost, and revenue from sales, to determine the optimum choice of final product. The comparison of net present worth and rate of return of all of the products proved that production of urea is the best choice for final product. Urea is most commonly used in fertilizers and is produced by reacting ammonia with carbon dioxide. Further analysis of the growing urea market displayed that the maximum plant capacity, in order to refrain from substantially affecting the current urea price, is a facility capable of processing 6,000 tons/day of MSW. At full capacity, this plant will produce approximately 1,960 tons/day of urea. Throughout the past decade, management of the 25,000 tons/day MSW produced has become a serious concern for New York City (NYC). Due to the large amount of waste generated and high disposal cost, NYC is an ideal location to apply this new approach to waste management. The terms of contracts between NYC and existing waste disposal facilities suggests that an expansion of 1,800 tons/day is possible for each year until the maximum plant capacity, 6,000 tons/day is reached. A drop charge to NYC of $40/day will provide the city financial relief compared to the current waste disposal methods. The total capital investment for a 6,000 MSW ton/day waste-to-urea facility is approximately $418 million. This project has a net present worth of $259 million with an expected rate of return of 21%. These economic results are more sensitive to fluctuations in urea price than the ability to operate at full capacity. The break-even urea price for this project is $60/ton. The following report provides the details of a manufacturing facility designed to process municipal solid waste, producing urea as the final product. The economic analysis that follows shows that this approach is a feasible and profitable solution to the municipal solid waste management crisis facing NYC.

1

Table of Contents

Municipal Solid Waste in the United States .............................................................................. 2

Municipal Solid Waste Disposal Methods ................................................................................. 4

Landfilling................................................................................................................................ 4

Front-End Processing .................................................................................................................. 7

Gas Cleaning................................................................................................................................ 9

Methanol................................................................................................................................... 10

Acetic Acid................................................................................................................................. 11

Formaldehyde ........................................................................................................................... 11

Dimethyl Ether .......................................................................................................................... 12

Hydrogen................................................................................................................................... 12

Ammonia................................................................................................................................... 12

Urea ........................................................................................................................................... 13

Synthetic Fuel............................................................................................................................ 13

Comparison of Products ........................................................................................................... 14

Demand ..................................................................................................................................... 20

Market Infiltration .................................................................................................................... 20

Total Capital Investment .......................................................................................................... 23

Operating Cost .......................................................................................................................... 23

Plant Size Selection ................................................................................................................... 25

Risk Analysis.................................................................................................................................. 26

Sensitivity Analysis ................................................................................................................... 26

Regret Analysis.......................................................................................................................... 27

2

Introduction The purpose of this project is to find a profitable alternative solution to the current municipal solid waste (MSW) disposal methods used in the United States. Current MSW disposal methods are landfilling and incineration. The alternative disposal method considered in this paper is pyrolysis, in which the municipal solid waste undergoes thermal decomposition to produce a synthesis gas. This gas can be used as a feedstock to create several different chemical products. Municipal Solid Waste in the United States Municipal solid waste includes all waste items produced residentially and commercially. Residential waste includes waste from single family and multi-family dwellings and accounts for approximately 60% of the total MSW produced. Commercial waste includes waste produced from businesses and schools and accounts for approximately 40% of the MSW produced. In 2005, there was approximately 245.7 million tons of MSW produced in the U.S., the majority of which was landfilled. According to the Environmental Protection Agency approximately 133.3 million tons of MSW was landfilled in 2005. In addition, incineration with energy recovery disposed about 33.4 million tons of the total MSW. The remaining 79.0 million tons of waste produced was recovered for either recycling or composting. Table 1 shows a breakdown of the disposal methods for the MSW waste produced in 2005.1

The composition of municipal solid waste is highly variable. It is typically composed of newspaper, product packaging, yard clippings, plastics, furniture, clothing, food scraps, glass, metals, appliances, and batteries.1 The average composition of discarded municipal solid waste is shown in the pie chart in Figure 1.1

Activity Amount

(millions of tons) % of Total Generation 245.7 100.0% Recovery for Recycling 58.4 23.8% Recovery for Composting 20.6 8.4% Total Materials Recovery 79 32.1% Combustion with Energy Recovery 33.4 13.6% Discards to Landfill 133.3 54.3%

Table 1. 2005 MSW Breakdown

3

Figure 1. MSW Composition

The production of MSW has steadily increased over the last 45 years from 88 million tons in 1960 to 246 million tons in 2005. However, over the last 15 years, the amount of waste that has been recovered has also increased. Due to increased recycling rates, the amount of waste that has been landfilled and incinerated has remained approximately constant at 160 million tons/year. Figure 2 shows the generation and recycling trends in the U.S. from 1960 – 2005.1

Figure 2. MSW Generation and Recycling Trends

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Municipal Solid Waste Disposal Methods Landfilling Because it is typically inexpensive relative to other disposal methods, landfilling is the most common for municipal solid waste in the United States. Landfills are ideally designed so that the waste can be buried in the ground and isolated from the surrounding environment. However, when water comes in contact with the waste, a leachate is produced. Leachate can contain metal ions, chloride, sulfate, nitrate, and various organic acids.2 If allowed to leak from the landfill site, these contaminants can infiltrate groundwater supplies. Newly built landfills use clay and synthetic liners to help isolate the waste and prevent leachate from polluting groundwater systems. Another consequence of landfilling is the production of landfill gas. Landfill gas consists of carbon dioxide and methane which are greenhouse gases. Significant efforts have been made at capturing landfill gas as a safety precaution and for energy usage. As shown in Figure 3, the number of landfills in the United States has been steadily decreasing over the last 18 years.

Figure 3. Number of Landfills in the U.S.1

Since the number of landfills has been decreasing and the amount of waste being landfilled has stayed approximately constant over the last several years, the sizes of landfills that are still in use are becoming larger. Generally, land available for landfilling is not a problem; however, in some densely populated areas of the United States there are problems with insufficient availability of landfill space.1 Figure 4 shows the number of landfills in 2005 by region in the U.S.

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Figure 4. Number of Landfills by U.S. Region1

The northeast has approximately 8% of the operating landfills in the United States. This region of the United States is faced with the most critical problem of declining landfill space and therefore typically faces higher disposal costs than other locations. In some cities, where there is virtually no available landfill space, MSW must be exported out of city limits. In extreme cases, it is exported to other states. The cost of landfilling varies widely depending on location, but it can be as high as $70/ton in some parts of New York City.

Incineration

Incineration is a process that uses heat to directly combust municipal solid waste to produce gas and residual ash. The direct combustion of waste results in the production of dioxins, mercury, lead, sulfur dioxide, nitrogen oxides, carbon monoxide, and carbon dioxide, some of which are toxic. Most of the combustion facilities in the United States incorporate energy recovery to help offset some of the operating expenses.1 Heat from the incinerators can be used to produce steam from water to generate electricity. The major benefit from incineration is the volume reduction of the waste. Incineration can reduce waste volume by up to 90% and total weight by 75%.3 In 2005, there were 88 operating waste-to-energy plants in the U.S. Approximately 44% of these facilities are located in the northeastern part of the United States. The northeast also has the highest capacity of waste incinerated per capita in the U.S.1 Figure 5 shows the incinerator MSW capacity per capita for the four major regions in the U.S.

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Pyrolysis An alternative method for managing solid waste is pyrolysis. Pyrolysis is the thermal decomposition of organic matter in the absence of oxygen. Gasification, a similar process, is the partial combustion of organic matter in a limited, or less than stoichiometric, amount of oxygen. The endothermic reactions involved in pyrolysis require a heat source, but gasification is thermally self-sustaining. By allowing these reactions to occur simultaneously, the exothermic combustion reactions from gasification can generate heat for the pyrolytic reactions. The terms pyrolysis and gasification will be used interchangeably throughout this report. Pyrolysis has a variety of benefits that set it apart from more conventional waste management methods: landfilling and incineration. One of the major products of pyrolysis is synthesis gas. Synthesis gas (syngas) is a gaseous mixture containing approximately 90% hydrogen, carbon monoxide and carbon dioxide. The other main components of syngas include methane, higher hydrocarbons and inerts. This syngas can be further processed to produce a variety of different products. Pyrolysis, as a waste management method, can be much more profitable due to the ability to produce a saleable end product from waste. Additionally, pyrolysis reduces the quantity and improves the quality of solid waste. This could remedy the problems associated with the lack of landfill space in many densely populated regions. Pyrolysis also has the ability to comply with more stringent environmental regulations than incineration.

Figure 5. Incinerator MSW Capacity per capita in the U.S.1

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Pyrolysis Process The Purox Pyrolysis system consists of three major sections: front-end processing, a pyrolysis reactor and gas cleaning. The front-end processing unit separates the heavy metal fraction and particulates from the organics and shreds the reactor feed. In the pyrolysis reactor, the solid waste feed is converted to synthesis gas. This gas is then purified, compressed and sent to another process system to be converted to the desired end-product.4

Figure 6. Pyrolysis Mass Balance

Front-End Processing A front-end loader coordinates transportation of the solid waste from trucks to a conveyer. This conveyer feeds waste to a shredder that reduces the particle size to between 4 and 8 in.4 The waste is then fed to the top of an air classifier, where air is blown countercurrent to the waste stream.5 The overhead stream is composed mostly of the less dense, organic fraction. This fraction flows to a cyclone separator to remove particulates. The air exits the top of the cyclone and is sent to a baghouse to be filtered and discharged to the atmosphere. The organic portion of the cyclone is sent to a surge tank, where it is held until it can be fed to the pyrolysis reactor. The heavy fraction exits the air classifier through the bottom and is sent to a magnetic separator capable of removing 90% of the ferrous in the feed stream. The remaining heavy fraction goes to an Eddy Current Aluminum Separator that removes 66% of the aluminum in the solid waste feed. The remaining heavy fraction is combined with the light fraction in the surge bin to be fed to the pyrolysis reactor.4,5

Syngas66.15 tons/unit time

Refuse Feed91.07 tons/unit time

Slag20.63 tons/unit time

Oxygen20.62 tons/unit time

MSW100 tons/unit time

Front-End Sorting and Shredding

PyrolysisReactor

Water26.63 tons/unit time

Metals8.93 tons/unit time

8

Pyrolysis Reactor

The Union Carbide Corporation Purox gasifier is an ideal reactor system for conversion of municipal solid waste to synthetic gas due to its ability to process feed with varying composition. The separated solid waste enters the vertical shaft reactor through the top and flows downward. Purified oxygen from an air separation unit is fed to the bottom of the reactor.6 The solid waste is dried by the upward flowing gases at the top of the reactor and then pyrolyzed in the middle zone. The pyrolytic reactions, shown below, take place at temperatures above 1500°C. In the bottom portion of the reactor, the oxidative zone, combustion of the char from the upper zone produces the heat necessary for the endothermic pyrolytic reactions.7 The gas exiting the reactor is cooled by the incoming waste to between 93°C and 315°C.4 The synthesis gas leaving the reactor contains fly ash, water vapor and some oil mist, which must be removed downstream. The solid inorganic products accumulate at the bottom of the reactor and mix with water to form a black glassy aggregate. This aggregate can be used for construction purposes.8 A typical composition of the syngas product from the Purox pyrolysis system is shown below in Table 2. An exact syngas composition can not be defined due to the variability of the incoming refuse composition.

Typical Synthesis Gas Composition4

Component Mole Percent, Dry Basis

H2 24

CO 40

CO2 24

CH4 5

C2H2 0.7

C2H4 2.1

C2H6 0.3

Higher

Hydrocarbons 2.35

Nitrogen 1

Argon 0.5

H2S 0.05

Moisture Content 6

Table 2. Typical Synthesis Gas Composition

COCOC

HCOOHC

COOC

22

22

22

→++→+

→+

kmolMJH

kmolMJH

kmolMJH

/173

/131

/406

=∆=∆

−=∆

9

Gas Cleaning The syngas flows through a spraying water scrubber and then to an electrostatic precipitator which removes solid particulates and pyrolytic oils. These components can be recycled back to the reactor. The gas flows through an acid absorption column where salts are neutralized and also sent back to the reactor. Finally, water is removed from the syngas in a shell and tube vertical condenser.

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Product Selection Synthesis gas can be used to produce many different chemicals and fuels. After considering several potential products, the economics of eight products were compared to determine the most profitable product. The following sections will show the total capital investment, total revenue, and total operating cost for a 1,500 tons/day MSW pyrolysis plant for each of these products. This analysis was then expanded to encompass a wide range of plant capacities. The net present worth (NPW) and internal rate of return (IRR) were the economic parameters used to determine the most profitable product. For this analysis, the tax rate, depreciation, cost of MSW front-end processing and revenue from collecting the municipal solid waste were neglected. It was assumed that these economic factors would influence the profitability of all of the products the same way, and therefore would have a significant impact on the outcome of the comparison. The following sections show the total capital investment, operating cost, product price, and product flowrate for each of the products. The calculations to arrive at the values reported were based on a municipal solid waste capacity of 1,500 tons/day. Methanol Methanol, the simplest alcohol, is a light, volatile chemical. It is typically used as an antifreeze, solvent, fuel, or as an intermediate in the production of other chemical products. Methanol is typically produced from synthesis gas. However, the synthesis gas is commonly formed from the methane in natural gas, by steam-methane reforming or partial oxidation. The chemical reactions to produce methanol from syngas are:

OHCHCOH 322 →+OHOHCHCOH 23223 +→+

Figure 7. Potential Products

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The conversion to methanol in these reactions is favorable at low temperatures and high pressures. The total capital investment and annual operating cost to produce methanol from 1,500 tons/day MSW, estimated from information found in The Encyclopedia of Chemical Processing and Design, were determined to be $82,317,331 and $8,612,836, respectively.9 A plant of this capacity would produce 13,739,742 gal/year of methanol. The current price of methanol, $1.015/gal, was reported on ICIS pricing.com.10 Acetic Acid Acetic acid is a weak carboxylic acid used to produce vinyl acetate monomer and acetic anhydride. It is also an important component in vinegar and can be used as a solvent. The Monsato process, commercialized in 1970, uses a rhodium-based catalyst to produce acetic acid from methanol by methanol carbonylation: In the 1990’s BP Chemicals developed the Cativa catalyst, capable of producing acetic acid from the same reaction, but doing so more efficiently and more environmentally friendly. This process is under license by BP, so the total capital investment and annual operating cost to produce acetic acid were estimated from a financial report for a Celanese acetic acid from methanol plant that uses the Monsanto process and the estimated cost of a methanol plant.11 These costs were found to be $141,194,727 and $34,751,576, respectively, for a plant processing 1,500 tons/day of MSW. A plant of this capacity would be capable of producing 170,202,384 lbs/year of acetic acid. The current price of acetic acid, $0.310/lb, was reported on ICIS pricing.com.12 Formaldehyde The simplest aldehyde, formaldehyde, is most often used to produce polymers and a wide variety of specialty chemicals. It is produced from the oxidation and dehydrogenation of methanol: The catalyst used to produce formaldehyde is typically silver metal or mixture of an iron oxide with molybdenum and vanadium. From information in The Encyclopedia of Chemical Processing and Design, the total capital investment for a formaldehyde plant producing 85,115,364 lb/year of formaldehyde from 1,500 tons/day MSW was determined to be $90,784,183.13 The annual operating cost for this facility would be $11,406,889. The current price of formaldehyde, obtained from Chemical Market Reporter, and used for the economic analysis was $0.21/lb.14

COOHHCCOOHCH 523 →+

OHCOHOOHCH 2223 222 +→+

223 HCOHOHCH +→

12

Dimethyl Ether Dimethyl ether is a gaseous ether most commonly used as an aerosol spray propellant or a refrigerant. It is produced from methanol dehydration: All sources of information regarding dimethyl ether manufacturing plants reported that these facilities are typically very small in scale, relative to the other potential products examined. The production rate of dimethyl ether from a plant processing 1,500 tons/day MSW would be 29,615 tons/year. A report prepared by Air Products and Chemicals, Inc., examining the market outlook for dimethyl ether, reported that the current dimethyl ether market is 143,000 tons/year.15 Therefore, a plant processing 1,500 tons/day MSW would produce enough dimethyl ether to satisfy 21% of the current market. It was assumed that attempting to take over such a substantial portion of the current market, without a substantial increase in demand, would likely have an unfavorable affect on the already low price of $0.06/lb.16 Therefore, the capital investment and operating cost to produce dimethyl ether were not researched and this potential product was assumed to be unprofitable. Hydrogen Hydrogen, a colorless, orderless gas, is frequently used for the processing of fossil fuels and to produce ammonia or methanol. Bulk production of hydrogen is usually accomplished by the steam reforming of natural gas. Hydrogen is one of the main components in synthetic gas produced from pyrolysis of municipal solid waste, constituting about 24% by volume of the gas. If hydrogen is the desired final product, the water-gas shift reaction would be used to convert the carbon monoxide to hydrogen and carbon dioxide: Following water-gas shift, the synthetic gas would have to be further purified in order to produce saleable hydrogen. The total capital investment and operating cost to produce hydrogen from 1,500 tons/day MSW were estimated using information gathered from The Encyclopedia of Chemical Technology.17 These costs were found to be $130,762,286 and $3,268,073, respectively. The current price of hydrogen, $0.08/m3, was estimated from this source as well.17 The annual production of hydrogen for a plant of this capacity would be 192,626,192 m3. Ammonia Ammonia is a colorless alkaline gas that possesses a characteristic, penetrating odor. It is one of the most largely produced inorganic chemicals. The largest market for ammonia is the fertilizer industry. The most common use of anhydrous ammonia is direct use as the nitrogen source in fertilizer. Another significant portion of ammonia use is in the manufacture of urea, another major fertilizer component. Ammonia is also used to

222 COHCOOH +→+

OHOCHCHOHCH 23332 +→

13

produce nitric acid and ammonium nitrate. Ammonia is produced using the Haber-Bosch process: This requires a hydrogen feed, typically coming from synthesis gas processed to increase hydrogen content and then purified (as described above for direct hydrogen production). The total capital investment for a plant processing 1,500 tons/day of MSW, $104,622,118, was estimated using information reported in the Encyclopedia of Chemical Processing and Design.18 The annual operating cost of this plant was estimated as $6,916,562, using process information provided in the Encyclopedia of Chemical Technology.19 A plant of this capacity would produce 97,137 tons/year. The current price of ammonia, obtained from ICIS Chemical Business Americas, is $275/ton.20

Urea Urea is typically a solid produced as prills or granules, for use in fertilizers. It can also be used in plastics manufacturing and as a protein supplement in animal feeds. Urea is formed by reacting ammonia with carbon dioxide. The intermediate formed in this reaction is ammonium carbamate. The total capital investment for a plant manufacturing urea from 1,500 tons/day MSW was estimated using information obtained from Ullman’s Encyclopedia of Industrial Chemistry.21 This cost was determined to be $137,284,159. The annual operating cost was estimated to be $9,006,088, which was based on process information provided in the Encyclopedia of Chemical Processing and Design.22 A plant capable of processing 1,500 tons/day of MSW would produce 171,418 tons/year of urea. The price of urea, $223/ton, was found in Chemical Market Reporter.23

Synthetic Fuel Synthetic fuel can be produced by the Fischer-Tropsch process in which synthesis gas is reacted over an iron or cobalt catalyst to produce liquid hydrocarbons. The synthetic gas that is used to produce synthetic fuel is usually produced through the gasification of coal or steam reforming of natural gas. The reaction for Fischer-Tropsch synthesis is The water gas shift reaction is used to make the synthesis gas have the ideal hydrogen to carbon monoxide ratio of 2:1. The Fischer-Tropsch process produces a wide range of liquid hydrocarbons and therefore further processing must be done before a final product is obtained. One of the most common products of synthetic fuel is diesel. Diesel that is produced from synthetic fuel is a high quality, low sulfur content diesel. It can be directly used as fuel source for diesel powered engines. Another product that is produced

OHCHCOH 222 --2 +→+

322 23 NHNH →+

OHCONHNHCOONHNHCONH 22242232 +→→+

14

from synthetic fuel is naphtha. Naphtha can be used as a feedstock to produce higher octane gasoline or in the chemical industry as a chemical feedstock. The total capital investment and operating costs to produce synthetic fuel from 1,500 tons/day MSW were estimated to be $93,765,169 and $5,207,041/year, respectively. These values were based on information from a Fischer-Tropsch design and economics paper written by members of the Bechtel Corporation and Syncrude Technology, Inc.24 It was estimated that approximately two-thirds of the syncrude could be refined into diesel, while the other third could be refined into naphtha. The price of diesel was estimated to be $1.98/gal, which was the average 2006 diesel price reported by the United States Energy Information Administration.25 The price of naphtha was estimated to be $1.63/gal, which was based on the August 2006 ICIS pricing report.26 The production rate for a plant of this capacity was 5,953,779 gal/year of diesel and 3,044,364 gal/year of naphtha. A summary of the production rate, product price, operating cost, net revenue, and total capital investment for each product is given in Table 3.

Product Production Price Operating Cost

Net Revenue Total Capital Investment

(unit/day) ($/unit) ($/year) ($/year)

Methanol (gal) 39,212 $1.02 $8,973,769 $5,555,679 $84,530,800

Acetic Acid (lb) 485,737 $0.31 $36,199,558 $18,761,628 $141,194,727

Formaldehyde (lb) 242,909 $0.21 $11,882,176 $6,736,810 $90,784,183

Ammonia (ton) 277 $275 $7,204,301 $20,620,952 $107,435,351

Urea (ton) 489 $223 $9,381,341 $30,437,687 $140,975,657 Hydrogen (m3) 549,732 $0.08 $4,013,046 $11,877,158 $130,762,286 Synthetic Fuel $5,207,041 $11,565,243 $93,765,169

Diesel (gal) 16,312 $1.98

Naphtha (gal) 8,341 $1.63 Table 3. Summary of Economic Parameters for Potential Products

Comparison of Products The previous sections discussed how the total capital investment, total operating cost, product prices, and production rate were obtained for each product based on 1,500 tons/day of MSW. These economic parameters were used to calculate the net present worth (NPW) and internal rate of return (IRR) for each product. Furthermore, the municipal solid waste capacity was varied to see how the NPW and IRR varied for each product. Plant capacity ratios were used to scale up the total capital investments for each increase in capacity. Plant operating costs were also updated to account for efficiencies

15

in having higher plant capacities. Figure 8 shows how the NPW changes for each product as municipal solid waste capacity increases.

Figure 8. NPW of Potential Products

For each product, excluding Methanol, the NPW increases with increasing municipal solid waste capacity. Based on NPW, urea is the most profitable product for all MSW capacities. The most profitable MSW capacity is 6,000 tons/day. The profitability of each product was also compared based on internal rate of return. Figure 9 shows how the rate of return changes for increasing municipal solid waste capacities.

16

Figure 9. IRR of Potential Products

Based on rate of return analysis, urea is the most profitable for almost all MSW plant capacities. Hydrogen production has a slightly higher rate of return than urea for a MSW plant capacity of 6,000 tons/day. However, based on the combination of net present worth and internal rate of return analysis, urea is the most profitable product from the pyrolysis of municipal solid waste.

17

Urea Synthesis Urea is the product formed in the reaction of ammonia with carbon dioxide. Therefore, the first process unit for urea synthesis must produce ammonia and separate carbon dioxide from the synthesis gas. Ammonia production from synthesis gas requires two chemical reactions:19

A process flow diagram outlining the ammonia production unit is shown in Figure 10. This diagram shows a mole balance based on 100 tons/day MSW processed. This balance was scaled up for analysis of larger capacities.

Figure 10. Ammonia Synthesis Mole Balance

The synthesis gas is first compressed after exiting the pyrolysis unit. The sulfur must then be removed because it will poison the catalyst used for ammonia synthesis downstream. This can be accomplished in a variety of ways. Due to the relatively small amount of sulfur that could be recovered in a sulfur production unit, a sulfur absorbent zinc oxide catalyst will be used to remove the sulfur.19 The remaining synthesis gas is compressed again, and then fed to a two-stage adiabatic water-gas shift reactor. The water-gas shift reaction serves to remove carbon oxides

322

222

3 NHNH

SynthesisAmmonia

HCOOHCO

ShiftGasWater

→+

+→+

Sulfur Removal CompressionWater-Gas

Shift Conversion

CompressionAmmoniaSynthesis

CO2 Removal

CompressedSynthesis Gas

2.55 x 106 moles/unit timeFrom Pyrolysis Unit

CO2

1.63 x 106 moles/unit timeTo Urea Reactor

N2

5.44 x 105 moles/unit timeFrom Air Separation Unit

Ammonia1.09 x 106 moles/unit time

To Urea Reactor Methanation

H2O

18

capable of deactivating the ammonia synthesis catalyst, maximize hydrogen production for ammonia synthesis and maximizing carbon dioxide production necessary for urea synthesis. The two-stage reactor consists of a high temperature converter and a low temperature converter. The majority of the carbon monoxide conversion occurs in the high temperature converter, and then the remaining portion reacts due to a more favorable equilibrium in the low temperature reactor.19

In the next step, carbon dioxide is removed as a pure stream to be fed to the urea process unit. The solvent methyldiethylamine (MDEA) is used as the absorbent to remove carbon dioxide. This solvent requires very low regeneration energy due to weak CO2-amine bonds.27 The next process, methanation, removes any remaining carbon monoxide by reaction with water to form methane.19 Nitrogen is added to the purified hydrogen gas at a 3:1 molar ratio. This gas is compressed to reaction pressure, between 2100 and 2200 psi, and fed to the reactor. The reactor contains a catalyst produced mainly from magnetite that has been promoted using alkali such as aluminum, calcium or magnesium. The reactor bed must be cooled because of the exothermic nature of the synthesis reaction. The ammonia is recovered from the reactor by condensation at synthesis pressure. The un-reacted gases are recycled back into the reactor in order to achieve higher conversions due to equilibrium limitations.19 Using a total recycle process, as is typical in industry, virtually complete synthesis gas conversion is achieved.33 Ammonia and carbon dioxide are fed to the urea synthesis reactor at a 3.5:1 molar ratio. Therefore, only 19 mol% of the carbon dioxide produced from the pyrolysis and subsequent water gas shift reactions is used for urea synthesis. The remaining carbon dioxide must be emitted or sequestered. The following reaction takes place, forming the desired product, urea, and ammonia carbamate as an intermediate:22 The reactor operates at a pressure of 2200 psi and temperatures between 185°C and 190°C to achieve high conversion and prevent corrosion resulting from production of the ammonia carbamate intermediate.22

OHCONHNHCOONHNHCONH 22242232 +→→+

19

Figure 11. Urea Synthesis Mole Balance

The carbamate is then decomposed in three vessels. The first is at reaction pressure, the second decomposition stage is at 260 psi and the third is at 66 psi.22 Ammonia and carbamate removed from the urea solution in these vessels are recycled back to the synthesis reactor to achieve virtually complete conversion of ammonia.34 The urea solution is then concentrated in an evaporator and proceeds to finishing, where the final prilled or granulated product is produced.21

20

Urea Market Demand The urea market remained relatively constant from 1999-2005, varying from 11.4 million tons in 1999 to 11.6 million tons in 2005.23 Figure 12 shows the U.S. urea demand from 1999-2005. The major driver for the urea market is the farming industry and therefore crop prices. Higher crop prices usually indicate that farmers are more likely to use more fertilizer in order to increase their crop yields. Approximately 41% of the urea sold is used on corn fields.23 Corn is the major feedstock for ethanol production, which is being used as an alternate energy source. Corn plantings increased over 4% from 2003-2005. Several reports from the Chemical Market Reporter indicate that ethanol production will increase due to the increased biofuel demand. This increase in ethanol production should result in an increase in fertilizer demand.28

Market Infiltration Figure 13 shows the percent of the 2005 U.S. urea demand as a function of MSW plant capacity.

U.S. Urea Demand

0

2

4

6

8

10

12

1999 2000 2001 2002 2003 2004 2005

Year

Dem

and

(M

Mto

ns)

Figure 12. U.S. Urea Demand

21

Figure 13. Percent of 2005 Urea Demand

It was assumed that the maximum market percentage that can be entered without significantly altering the urea price was estimated to be 7%. This percentage of the market corresponds to a MSW capacity of 6,000 tons/day. Based on mass balances and process conversions reported in literature, a plant of this capacity will produce approximately 2,000 tons/day of urea. The net production of carbon dioxide from this process is 3,485 tons/day, which as stated previously, must be either emitted or sequestered.

22

Plant Location In a request for information released in 2004, the New York City Department of Sanitation asked for proposals of new, innovative methods to manage the nearly 25,000 tons of MSW generated by the city each day.29 New York City currently does not have landfills, incinerators or resource recovery facilities to handle the waste produced. As a result, about seventy percent is exported to out of state landfills, making the state of New York the largest exporter of solid waste in the country.30 Furthermore, the continuously growing population in New York City will add to this problem in the near future. The waste-to-urea facility proposed in this report would provide relief for New York City’s waste management crisis. The MSW in New York City is currently transported to transfer stations in surrounding cities and states. From these transfer stations the waste is taken to out-of-state waste disposal facilities. This currently costs the city an average of $70/ton of MSW. The contracts between the transfer stations and the city of New York, designating the amount of waste accepted and disposal charge, are agreed upon for three year terms with two one year renewal options.31

Available TPD from Expiring Contracts

2000 2001 2002 2003 1700 2500 3160 2350

Average 2428 Standard Deviation 599 Annual Expansion Opportunity 1800

Table 4. Available MSW Expansion Capacity (tons/day)

The MSW available in tons/day due to expiring contracts for the years 2000 to 2003 are shown in Table 4. The average amount of MSW that became available each year during this period is 2,428 tons/day, and the standard deviation of this value is 599 tons. In order to conservatively estimate the expansion opportunity available due to expiring contracts for a waste-to-urea facility in the New York City area, it was assumed that the annual expansion opportunity would be at least one standard deviation less than the mean, or 1,800 tons/day. This expansion opportunity will allow the proposed 6,000 tons/day plant to reach its maximum capacity by the fourth year of operation. Based on the current average drop charge, $70/ton, paid by New York City for disposal of MSW, a charge of $40/ton should be charged by the proposed waste-to-urea plant. This choice would be low enough to make the proposed waste management approach an appealing alternative to the city’s current methods, while still producing favorable economic results.

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Economics for Urea Production Total Capital Investment The total capital investment for the Urea plant was discussed previously in the product selection section of this paper. The addition of a front-end processing plant was added to calculate a total capital investment for the urea plant. Figure 14 shows how the total capital investment increases with increasing plant capacity.

Figure 14. Urea TCI

The total capital investment increases almost linearly with increasing MSW capacity. The total capital investment for a 6,000 tons/day MSW plant is approximately $418 million. Operating Cost The total operating cost for the production of urea was calculated using various literature sources for ammonia, urea, and pyrolysis plants. Utilities, labor, and catalyst costs were estimated directly from plant examples in the Encyclopedia of Chemical Technology.34 The other operating cost parameters were estimated using percentages provided in Plant Design and Economics for Chemical Engineers.32 Supervision was estimated as 15% of the labor costs. Maintenance and repairs were estimated as 3% of the fixed capital investment. Operating Supplies were estimated as 15% of the maintenance and repair costs. Laboratory charges were estimated as 15% of the labor cost. Insurance was estimated as 0.7% of the fixed capital investment. Property taxes were estimated as 2% of the fixed capital investment. Overhead was estimated as 60% of the labor, supervision, and maintenance and repair costs. Administrative costs were estimated as 20% of the labor, supervision, and maintenance and repair costs. Distribution and

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marketing costs were estimated as 6% of the total operating cost. The breakdown of the total operating cost for producing Urea from a MSW feed of 6,000 tons/day is shown in table 5.

Direct Cost $/ton of Urea Utilities steam (103-104 kPa), m3 12.84 cooling water, m3 13.95 Labor, personnel shift ($28/h) 5.72 Supervision 0.86 Catalyst cost 2.31 Maintenance and Repairs 14.92 Operating Supplies 2.24 Laboratory Charges

0.86

Fixed Cost Insurance 3.48 Taxes 9.95 Overhead

12.90

General Cost Administrative Costs 4.30 Distribution and Marketing Costs 5.4

Total Operating Cost 89.74 Table 5. Urea Operating Cost32,34

The operating cost varies depending on the MSW capacity of the plant. As the capacity of the plant increases, the operating costs per unit mass decreases. This is due to operating efficiencies obtained by having an increased capacity. Figure 15 shows how the operating cost varies with capacity for a urea production plant.32,34 It appears that these costs will eventually reach an asymptote where changes in the capacity will no longer have a significant affect on the operating cost.

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Figure 15. Urea Operating Costs

Plant Size Selection The net present worth and internal rate of return were determined for varying plant capacities. For this analysis it was assumed that plants will be built to their maximum capacity prior to start up and the capacity of the plants would increase at the previously estimated rate of 1,800 tons/day per year until operation at maximum capacity is achieved. The net present worth and internal rate of return increase for increasing capacities, as shown in Figures 16 and 17. Based on the potential market for urea, it was estimated that the maximum amount of urea that could be produced and sold without adversely affecting the current market price of urea would be approximately 2,000 tons/day, which is equivalent to a solid waste capacity of 6,000 tons/day. Therefore, the most economical urea plant would be a 6,000 tons/day MSW plant. This plant would begin operation in 2009 at a capacity of 1,800 tons/day MSW. By the year 2012 the urea plant would reach maximum capacity at 6,000 tons/day.

Figure 16. Urea NPW Figure 17. Urea IRR

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Risk Analysis Sensitivity Analysis The two major factors that can affect the profitability of urea production are the municipal solid waste processed and the urea price. A sensitivity analysis was performed for each of these factors based on a 6,000 tons/day MSW plant. Figure 18 shows how the net present worth for the urea plant changes based on changing amount of municipal solid waste processed. For this case the urea price was held constant at $223/ton.

Figure 18. Sensitivity to MSW Capacity

From Figure 18, it was determined that processing 3,200 tons/day would be required to maintain an economical project. This is based on being able to increase the amount processed by the previously estimated rate of 1,800 tons/day per year. Similarly, a urea price sensitivity analysis was also performed for a 6,000 tons/day MSW plant as shown in Figure 19. In this case, the price of urea was varied while the other economic parameters were held constant.

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Figure 19. Sensitivity to Urea Price

From Figure 19, it was determined that the minimum price to maintain an economical project is approximately $87/ton. This is based on a 6,000Based on the slopes of both graphs, it is apparent that the net present worth of the urea plant is more sensitive to changes in the urea price. A break-even urea price was calculated to determine the minimum price that urea could be sold at in order to recover the total capital investment, with no profit. The break-even urea price for a 6,000 tons/day MSW plant was determined to be $60/ton. This break-even price was found by finding the price of urea that resulted in a net present value of $0 at a discount rate of 3%. This discount rate was chosen to account for the time value of money over the life of the project. Regret Analysis A regret analysis was performed using three different designs and three different scenarios. The three designs were plants with municipal solid waste capacities of 1,200, 3,500, and 6,000 tons/day. For plant sizes large than 1,800 tons/day MSW, the rate of MSW processed was increased annually up to the maximum capacity as previously described. The three scenarios were based on different urea prices of $121/ton, $223/ton, and $267/ton. These values were chosen based on the variability in urea prices described in recent market analysis articles. Table 6 shows the net present worth of each plant design for each scenario. These values were used to calculate the regret for each design as shown in Table 7.

NPW Design $121 $223 $267 Average

1 (1200 tpd) ($50,537,278) $7,657,043 $32,760,475 -3,373,253 2 (3500 tpd) $799,116 $170,532,552 $243,750,896 138,360,855 3 (6000 tpd) $97,473,595 $388,445,199 $513,962,361 333,293,718

Table 6. NPW

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Regret Design $121 $223 $267 Max

1 (1200 tpd) 148,010,873 380,788,156 481,201,885 481,201,885 2 (3500 tpd) 96,674,479 217,912,647 270,211,465 270,211,465 3 (6000 tpd) 0 0 0 0

Min 0 Table 7. Regret Analysis

By taking the minimum value of the maximum regret for each design, it can be determined that the 6,000 tpd plant is the optimum choice for the urea plant design. Furthermore, this regret analysis reiterates that a higher plant capacity will result in more favorable economics.

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Conclusion and Recommendations Pyrolysis, for municipal solid waste management, has a variety of benefits as an alternative to landfilling and incineration. The most likely benefit that could result in implementation of this approach is its ability to be profitable. The economics of a MSW pyrolysis facility is dependent on the end product produced. A wide array of different end products were examined, based on estimates of total capital investment, operating cost, and revenue from sales, in order to determine the optimum choice of final product. The comparison of net present worth and rate of return of all of the products proved that production of urea, an important component in fertilizers, is the best choice for final product. Due to the large amount of waste generated (25,000 tons/day) and high disposal costs, New York City would be an ideal location to apply this new approach to waste management. A drop charge to New York City of $40/day will provide the city financial relief compared to the current waste disposal methods. Further analysis of the urea market displayed that the maximum plant capacity is a facility capable of processing 6,000 tons/day of MSW. At full capacity, this plant will produce approximately 1,960 tons/day of urea. The total capital investment for a 6,000 tons/day waste-to-urea facility is approximately $418 million. This project has a net present worth of $259 million with an expected rate of return of 21%. These economic results are more sensitive to fluctuations in urea price than the ability to operate at full capacity. The break-even urea price for this project is $60/ton. The results show that producing urea from municipal solid waste is a feasible and profitable solution to the municipal solid waste management crisis facing New York City. Therefore, additional analysis of this approach is recommended to further support project implementation. A more detailed process design, including equipment sizing and costs, would provide a more accurate estimate of the total capital investment and operating cost. A study on the environmental impacts of this facility is also necessary to verify that no problems will arise from increasingly stringent environmental regulations.

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