Executive Summary:

Davis Corporation contracted jEO & Associates to analyze the profitability of constructing a new ethylene oxide plant. Additionally, jEO was charged with the task of designing the most profitable reactor system if market conditions are indeed promising. Davis Corporation projected that the plant can be constructed in two years and that the market demand at this time will be approximately 150,000 tons/year.

After a preliminary analysis, jEO determined that market conditions were favorable enough to make a new EO plant sufficiently profitable. Following extensive research, the direct-oxidation process using pure oxygen and the typically used silver/alumina catalyst was chosen and a detailed design was constructed. The recommended design requires a capital investment of $9.3 million, operates on any annual cost of $92 million and is projected to yield a $350 profit in present day dollars after 15 years of production (17 years after construction begins). jEO recommends that construction of these facilities begin immediately.

Table of Contents: 

Introduction

Ethylene Oxide Importance (Marketing Analysis)

EO Production in Industry

Direct Oxidation Process

Air-based vs. Oxygen-based Process

Safety and Environmental Issues

Overview of Process

Process Details

Reactor Feed Preheat/Effluent Cooler

Reactor

Reactor Chemistry

Catalyst

Design Details

Cooling Water

Materials of Construction

Absorber Section

Compressor Train

Utilities

Safety Concerns

Piping

Flanges, O-Rings, and Packing

Pumps

Valves

Insulation

Relief Systems

Storage and Transportation

Vent Gas Scrubber

Prevention of Backflow

Operability

Economics

Total Cost of Analysis

Conclusions

Introduction:

Ethylene Oxide Importance (Market Analysis)

Many companies produce ethylene oxide (EO), an important commodity chemical. A small portion of the direct ethylene oxide product is used as a general disinfectant of finer instruments, sterilizer for medical purposes, and as a fumigant in the spices industry (10). Approximately 98% of ethylene oxide is further processed to make the chemicals tabulated in Figure 1 (adapted from reference 15). Since ethylene oxide is an essential component for these consumer products, ethylene oxide will continue to be in high demand into the new millennium.

The Gulf Coast area is an ideal location for a new ethylene oxide plant. This is an area of continuous growth for the chemical and petrochemical industries. Since there are many chemical industries producing necessary chemical feedstock for ethylene oxide production, choosing this location for the future plant will allow for easy availability and transport of feed. The current available pipelines in the south allow for easy accessibility of chemicals. This area is also ideal for the ethylene oxide sales and distribution. Many companies in this area use ethylene oxide to produce other chemicals. Since the plant will be available for the surrounding companies, the outlook projection for the ethylene oxide business is high. If shipment of the product is necessary, the many waterways in the area allow for easy transportation to domestic and international businesses.

A Union Carbide representative describes the current ethylene oxide market as being slightly low this year (13). Since prices are slightly lower and competition for ethylene oxide production is low, the current year is an ideal time to begin development and construction of the plant. Market predictions indicate that the demand for EO will increase in approximately two years. Development of a new EO plant this year will result in a start-up in approximately two years, as the market embarks on an upswing in demand for EO.

EO Production in Industry

Ethylene oxide production is an old process that has gone through one major change throughout its life. The basic goal is still the same, to react ethylene and oxygen either directly or indirectly to produce ethylene oxide and several undesirable by-products. Initially, this was accomplished by the World War I era chlorohydrin process. In modern times, EO is produced by the direct oxidation of ethylene.

Direct Oxidation Process

Lefort was the first to synthesize ethylene oxide through the direct oxidation of oxygen and ethylene in the early 1930’s. This process became popular commercially, and still is the most common method of making ethylene oxide.

Ethylene Oxide Synthesis

Ethylene Combustion

The reactions above govern the direct vapor-phase oxidation of ethylene to ethylene oxide over a silver catalyst. The main byproducts of the reactions are carbon dioxide and water. Two other side reactions also occur in the reactor, which are the isomerization of acetaldehyde and production of formaldehyde. This initial proposal does not account for the amounts of these two products, typically less than 0.1% acetaldehyde and even less formaldehyde in the total amount of reaction products (12). This design process uses the direct oxidation process to synthesize ethylene oxide.

Air-based vs. Oxygen-based Process

Different industries use either air or oxygen as feed streams to obtain an oxygen source to react ethylene with oxygen. jEO & Associates need to consider whether to use air or oxygen for its source of oxygen feed. The oxygen-based process is chosen due to its many advantages. For all plant capacities and a given type of catalyst, the oxygen-based reactor yields a higher selectivity and requires less catalyst (10). Although the air-based process may cost lower to run (for small to medium-sized plants), the initial building costs of the air-based plant is much more than the oxygen-based plant (10). While the oxygen-based process requires a carbon dioxide removal section, more stainless steel, and some expensive instrumentation, the air-based process requires more catalyst, more reactors (to achieve a comparable selectivity), a multi-stage compressor, air purification units, a vent gas treating system, and two to three reactor train in series (12).

In spite of the extra equipment for the air-based process, the production level of ethylene oxide for an air-based process is still less than the oxygen-based process. The average selectivity ranges from 65-75% compared to 70-80% for the oxygen-based process. Furthermore, the oxygen-based plants can have a yield of up to 0.1 kg ethylene oxide per kg ethylene more than the air-based plants (12). Due to this reason, the oxygen-based process is a more attractive choice.

The air-based process has the gas purge stream, which contains ethylene that requires extra treatment before it can be vented to the atmosphere. This extra air pollution is not part of the oxygen-based process (5). The cycle gas purge stream of the oxygen-based process is usually small enough to be burned without too many pollution problems (8). The pure oxygen process poses less potential problem for the air.

Since the silver catalyst is expensive, the length of catalyst life is an important consideration. For the oxygen oxidation, the catalyst lasts longer and less is required for the catalyst charge (12). The air-based oxidation generally needs 1.5 times the catalyst charge of the other process. The required amount of catalyst and length of catalyst life also makes the oxygen-based process a more economically viable choice.

Safety and Environmental Issues

In the gaseous state, ethylene oxide easily condenses into liquid state at low temperatures. It is miscible with water, alcohol, ether, and most organic solvents (10). As a vapor, it is very flammable and explosive. Due to the highly strained cyclic structure of an ethylene oxide molecule, it is a very reactive compound. Plant hardware must be carefully chosen to avoid accidents and injuries. Caution must be used in the production process, storage, handling and transport of the chemical (5).

Ethylene oxide is the simplest cyclic ether, which is colorless as a gas and liquid. At higher concentrations, it can be detected by a slightly sweet smell. It can decompose even in the absence of air or oxygen. At certain temperatures, ethylene oxide will polymerize, releasing approximately 900 Btu/lb of reactant. Since rust and strong alkali are the catalysts for this exothermic reaction, the plant process must be designed so that ethylene oxide does not come in contact with those substances.

Direct skin contact results in blistering and severe skin damage, depending on how long the contamination occurs. Ethylene oxide can penetrate leather, particular kinds of rubber, as well as cloth. These items must be removed from the body immediately if exposed to the chemical. Short-term inhalation effects of ethylene oxide include drowsiness, disorientation, nausea, limb weakness, vomiting, and convulsions. These temporary conditions of ethylene oxide disappear within a few days after the limited chemical exposure. The action level of these effects include 0.5 parts per million over an eight hour time-weighted average (3).

Even in lower concentrations, long-term exposure of ethylene oxide leaves lasting effects on humans. The chemical is generally regarded as dangerous for the central nervous system, reproduction, genetic effects, and cancer (3). Laboratory research has shown the substance to increase the risk of leukemia, stomach, and brain cancer in animals. Ethylene oxide has also been shown to decrease the reproductive activity of laboratory rats and mice. Studies cite the chemical as especially harmful to the male reproductive system, as it causes lasting mutations.

Since ethylene oxide is highly reactive, it does not remain in the environment for long following an accidental release or leak. Hydrolysis of the chemical (resulting in ethylene glycol) only occurs in more acidic solutions and specific temperatures. Studies have shown that ethylene oxide and its derivatives biodegrade to approximately 53% in a span of twenty days (3). The effects of these chemicals are moderate to plants, microorganisms, and fish, causing some mutagenic and toxic effects (5). Ethylene oxide spilled into the soil eventually evaporates, especially if the soil is saturated with rainwater. In water systems, the substance will simultanaeously evaporate and mix with the water at the surface. Overall, due to the high reactivity level, the possible release of ethylene oxide does not pose many threats to the environment.

Overview of Process:

The design models a process based on a four-part system developed by the conventional Shell direct oxidation technology. This basic design contains the following parts: the reaction system, absorption system, CO2 Removal Section, and EO purification system. This proposal focuses on developing and optimizing the reactor system.

The reaction system involves four shell-and-tube packed plug flow reactors, which contain silver/alumina catalyst. The feed flows are high-purity grade oxygen and ethylene. The catalyst eases the partial oxidation of ethylene to ethylene oxide and the complete combustion of ethylene to carbon dioxide and water. The selectivity of the ethylene oxide formation is around 81%, while the ethylene conversion to EO is around 10%. Since the reactions are exothermic, water is used as a cooling medium on the shell side of the reactor and is later used to produce large quantities of low-pressure steam.

In jEO’s design, the absorption system and CO2 Removal section is included with the reaction system in order to produce a realistic model of the recycle stream feed for the reactor. Since these areas were not within the scope of the project, the absorption of EO and water and the removal of CO2 were assumed to be ideal, with 100% removal of EO, and 100% removal of the total amount of CO2 flowing through the CO2 removal section.

The simplified and detailed design can be seen in the Figures 2 and 3 on the following pages. Additionally, the detailed process information can be found in the Appendix. It contains all stream data and information for a typical reactor.

Process Details:

Reactor Feed Preheat/ Effluent Cooler

The Pre-heat exchanger’s main purpose is to pre-heat the inlet feed from 181^oF to 266 ^oF. This is accomplished efficiently by pre-heating the feed in the tube side while simultaneously cooling the reactor effluent from 482^oF to 408^oF. The pre-heat temperature is selected based on previous research performed by a previous engineering team, EO and Sons, studying ethylene oxide production. Although a high reactor inlet temperature is desired, EO and Sons concluded that the heat exchanger surface area needed for any higher temperature required the use of an excessive amount of large and costly heat exchangers. The heat exchanger pressures are determined by the optimal reactor pressures. The tube side inlet pressure is 261 psia, and the shell side inlet pressure is 243 psia. The pressures are determined by the reactor pressure requirements.

Stainless steel is chosen for both the tube and shell sides because there is a large amount of EO flowing through the shell and possible trace amounts of EO in the tube side. EO is very reactive with rust and thus the use of stainless steel is critical to avoid a hazardous situation.

Reactor

Reaction Chemistry and Kinetics

Two reactions for ethylene oxide production were considered for the reactor system, which can be seen in Table 1. The main reaction is the formation of ethylene oxide from ethylene, with approximately 81% selectivity towards this reaction. The second reaction is the combustion of ethylene to carbon dioxide. The specifications for the system were to obtain approximately 10% conversion of ethylene and a 30-50% conversion of oxygen within the selectivity range stated.

The kinetics of the system are determined in order to begin the design of the reactor. Through the use of Arrhenius kinetics, the reactions are modeled based on given activation energies from literature (7). Pre-exponential factors need to be obtained in order to complete the kinetic design. The pre-exponential factors are determined using an iterative method. First, a base case is built in HYSYS in order to calibrate the reactor design. The Soave-Redlich-Kwong equations of state are selected since they are commonly used, and all simulated components are compatible in this set for HYSYS. Literature values are needed to obtain an idea of the total reactor tube volume to reactor inlet flow rate ratio. These figures are necessary to obtain an estimate for the residence time associated with typical literature values for conversion and selectivity. Since literature usually provides product flow rate to reactor volume correlation, a conversion reactor is used to solve for the inlet flow rate to reactor volume ratio. This type of reactor simply performs a mass and energy balance given the individual conversions for each reaction. With a residence time, inlet flow to reactor volume ratio and kinetic data obtained from Kenson (7), the pre-exponential terms are solved for a typical industrial reactor. These values are used to develop a plug flow kinetic model to replace the conversion model. The following table shows the kinetic data for the reactor:

These values allow for the selectivity and conversion to stay within range, allowing selectivity of the ethylene oxide formation to be high, while obtaining a relatively low conversion per pass. The selectivity of the synthesis reaction is maintained at around 81%. Approximately 12% of the ethylene is converted per pass, while 40% of the oxygen is converted.

Catalyst

The catalyst is an important part of the reaction mechanism because it determines the heterogeneous kinetics. Silver/alumina catalyst is the type of catalyst used, which drives the selectivity of the reactions towards ethylene oxidation. The silver allows for oxygen adsorption on its surface, which forms an ionized superoxide. The ethylene is reactive with this superoxide, resulting in the formation of ethylene oxide (4).

Although there are several variations of silver/alumina catalyst available, average values provided in the literature are used. Unfortunately, data on specific catalysts is proprietary and very difficult to obtain. This situation did not allow for any reliable or supportable comparisons between catalysts. jEO therefore models the catalyst in a manner to produce conservative results and uses catalyst properties consistent with the literature values for the classic Shell direct oxidation catalyst. This catalyst is capable of producing the 12% conversion and 81% selectivity desired. The change out time for this catalyst is approximately three years. One catalyst that jEO feels should be studied in the future is a fairly new catalyst that is capable of 86-87% selectivity with a reduced change out time of one year. Due to time and data constraints, jEO is not able to provide a satisfactory evaluation of this option.

Catalyst physical properties are modeled since they play a significant role in reactor performance and pressure drop. A higher catalyst density leads to an increased reaction rate, but unfortunately produces a higher pressure drop. Therefore an accurate representation of the catalyst properties in the model is crucial to obtaining accurate results.

The following table shows the details of the catalyst sizing that are used in the reactor:

The results obtained with these catalyst properties are in line with the literature values. The pressure drop in jEO’s model is 14.2 psia. Industry correspondance states that a typical pressure drop across a reactor should be between 10-20 psia (13). Therefore, the model appears to be reasonable in regards to yet a third parameter in addition to conversion and selectivity.

Design Details

Vertical plug flow shell-and-tube reactors are used for the system. Plug flow reactors are the most common reactors currently being used in industry for ethylene oxide production (13), since they allow for high velocities to be used and require less volume than other types of reactors. Since the reactions are exothermic, a shell-and-tube reactor design is ideal because it allows for coolant to be run through the shell side for heat exchange. This is critical in reducing hot spot formation, and more importantly in preventing the reactor temperature from running away (4). Hot spots cause severe catalyst degredation, and runaway temperatures can lead to catastrophic process failures. Therefore, the process feed flows through the tube side, while the cooling medium flows through the shell side. The reactors are vertical in order to provide back pressure for the system. This helps to keep the catalyst in place.

The parameters of the reactors are determined based on achieving the objectives of approximately 10% ethylene conversion and 81% selectivity. These values are typical in the literature and have been proven to yield an efficient consumption of the reactants. Using the developed kinetic model for the dominant reactions, the reactor parameters are optimized. jEO’s design includes a total of four reactors that are run in parallel. This design is superior to one large reactor because smaller reactors are less expensive to construct. Furthermore, this design allows for a smaller and less expensive spare which is crucial to reduce the threat of unexpected business interruptions. Each of these reactors contain 1712 tubes, which are 38 ft long and have a 0.13 ft inner diameter and a wall thickness of 0.017 ft. The tube diameters are consistent with the industry standard, and the number and length of the tubes are determined by rigorous simulation in HYSYS. These two parameters are selected in order to obtain the desired conversion and selectivity while maintaining an acceptable pressure drop.

It is determined that the inlet temperature should be 268 ^oF (based on preheat exchanger limitations—see Reactor Feed Preheat/Effluent Cooler section) with an outlet temperature of 482 ^oF. The reactor operates at 231 psia. Literature sources indicate that typical reactor conditions are with temperatures of 230-260 ^oC and pressure at around 147-367 psia (12) The feed contains ethylene at 99.5% purity and oxygen at 99.5% purity. The inlet is 33% ethylene and 8% oxygen.

The following table gives the reactor inlet and outlet conditions and compositions:

Cooling Water

The highly exothermic reactions require an effective cooling medium in the shell side of the reactor to prevent runaway reactions and hot spot formations. The chosen cooling medium chosen is water, which enters the reactor at 187 ^oF and leaves at 366 ^oF in the form of steam. According to JChem, this method of cooling provides the best heat transfer (4).

The cooling water requires a pump system to propel the water into the shell side of the reactor. This pump system provides the necessary cooling water to each of the four parallel reactors to remove the heat generated by the very exothermic reaction. Four separate pumps (one for each reactor) transport a total of 75,189 lb/hr of cooling water. This arrangement delivers an equal amount of cooling water to each reactor and reduces the risk of complete failure associated with the use of a single large and very expensive pump. It is unlikely that four pumps should fail or simultaneously need replacements. Therefore, a less expensive, smaller pump can be used as a universal spare. Additionally, repair expenses are not as high for smaller pumps.

Materials of Construction

Stainless steel is chosen the tube side and carbon steel is chosen for the shell side. There is a large amount of EO flowing through the tube side. Since EO is very reactive with rust, the use of stainless steel is critical to avoid a hazardous situation. Cooling water is flowing through the shell, therefore carbon steel is suitable.

Absorber Section

The reactor effluent leaves the reactor train and moves into the absorber area, with a great deal of inert gases and unreacted ethylene. From the reactor, the process flow enters the EO absorber, where water removes the EO from the stream. The EO exits through the bottom of the absorber and enters further separation and purification steps. These further steps are not within the scope of this proposal. The remaining components leave through the overhead of the absorber. A portion of this overhead stream enters the CO2 removal system. This stream serves as the recycle at the beginning of the process. Part of the overhead from the EO absorber completely bypasses the CO2 removal system and joins the recycle stream. The vent purges a small fraction of the inerts in the EO absorber overhead (to prevent build up of inerts in the stream).

Compressor Train

The compressor train increases the pressure of the recycle stream returning to the reactor inlet, in order to achieve the reactor inlet pressure conditions. The compressor train increases the pressure of the stream from 223 psia to the reactor inlet condition at 261 psia. A two-stage compression train consisting of rotary compressors accomplishes this goal. When compared to other units such as axial, reciprocating, and centrifugal compressors, this type of compressor is a suitable and very economical choice. Additionally, two-stage compression is more economical as the use of a single, much larger compressor is very expensive due to the large pressure increase it must produce. The process requires compressors that are sized to achieve approximately 75% adiabatic efficiency and 75% polytropic efficiency.

Utilities:

The reactor inlet preheater warms the reactor inlet from 181^oF to 266^oF, which requires a duty of 2.33e7 Btu/hr. This heat exchanger also serves to remove approximately 2.33e7 Btu/hr of heat from the reactor effluent stream, which cools the stream from 482^oF to 408^oF.

The cooling water system around the reactor serves to remove heat released by the reaction. This heat removal decreases the reactor effluent temperature to 482^oF. The heat removal required is a duty of 8.66e7 Btu/hr. This extra heat vaporizes the cooling water from 187^oF to 365^oF. The heat duty requires a cooling water flow of 75,200 lb/hr. The water comes from an external source. This amount of water requires 4.72e4 Btu/hr (13.8 kW), which is provided by electricity.

The compressor performs work on the recycle stream to increase the pressure of the stream from 223 psia to 261 psia. Two-stage compression, which uses electricity, provides the work. The first stage involves a compression from 223 psia to 242 psia. This requires 3.15e6 Btu/hr (920 kW). The second stage of compression increases the pressure from 242 psia to 261 psia. This requires 2.97e6 Btu/hr (872 kW).

Table 5 lists the total utilities used:

Safety Concerns:

Piping

Pipelines are specifically dedicated to transportation of ethylene oxide, due to the potential hazards of servicing the system for multiple substances. Since carbon steel can potentially rust (which leads to other reactions of ethylene oxide), the pipelines are constructed of austenitic stainless steel (Type 304). Copper, silver, magnesium, mercury and cast irons are not recommended for equipment servicing ethylene oxide due to low ductility, acetylenic materials, or high corrosion rates (3). The design of the piping system minimizes low points and stagnate dead spots, to also avoid the polymerization reaction (6). Furthermore, the surface area of the pipe sizes will be limited by keeping the diameter and length relatively short. High surface areas tend to lead to more polymerization of the product. Pipelines are kept short by utilizing a gravity drainage system where the line can be purged with nitrogen.

Flanges, O-rings, and Packing

The piping system is designed with very few flanges. At each flange, there is a potentially hazardous leak, which could lead to dangerous reactions in the atmosphere. The gasket material of flanges are spiral wound stainless steel with either Teflon filler or Grafoil GTB filler. The exact filler material of each flange are chosen according to the temperature of the substance passing through, since teflon is only chemically resistant to ethylene oxide up to 400-500 degrees Farenheit. For the same reason, o-rings are made of Kalrez 2035, virgin Teflon, or Chemrez 505. Only Teflon or Grafoil GTB are for the packing material (3).

Pumps

Only carbon steel, stainless steel, or ductile iron pumps are used in the process. Based on past experience, centrifugal pumps with double mechanical seals are used. The seal fluid is a 50% aqueous solution of ethylene glycol, due to its low reactivity when in contact with ethylene oxide. The pumps are strategically placed in curbed spots, isolated from direct process or storage units. This decreases the risk of potential overheating, leading to ignition of ethylene oxide vapors (3).

Valves

Valves are selected to avoid stagnate ethylene oxide in any valve openings. As in the pipelines, these dead areas can lead to polymerization of the chemical. For this reason, ball valves and plug valves are not recommended for ethylene oxide service. Furthermore, possible emissions of specific valve designs should also be considered (3). Gate valves, globe valves, and butterfly valves are installed at the necessary locations in the pipelines.

Insulation

The external walls of pipelines and vessels should be protected against excessive heat, due to the possibility of ethylene oxide decomposition. Insulation materials should be selected based on low corrosion rates, resistance to exothermic reactions of ethylene oxide, and durability under fire flames. In consideration of these issues, cellular foamglass are used as insulation since it is a closed cell material (decreasing the risk of trapping water, which leads to exothermic reactions).

Relief Systems

The pressure relief system are designed to tie into an overall system, which feeds to a flare. This reduces the risk for potential exposure to people in the surrounding area. A careful analysis of the system is performed, and relief mechanisms are designed for storage units and piping (where stagnant liquid can gather). The relief system is designed to avoid any possible plugging due to polymerization. The following factors are considered (3):

• Stainless steel piping
• Installation of rupture disks underneath relief valves
• Decrease the distance between relief valves and equipment units
• Adding nitrogen to the relief valve system periodically

Storage and Transportation

Upon production of ethylene oxide, it is transported by a railcar to a storage area. From the railcar, the substance is pressurized with an inert gas, such as nitrogen, and pumped into the temporary storage tank before it is used for further chemical processing (4). The storage vessels are designed according to ASME specifications and constructed of stainless steel (Type 304). The tanks are externally coated to avoid the possibility of long-term stress corrosion due to exposure to atmospheric chlorides. The railcars and storage units are exclusively used for ethylene oxide to reduce the risk of contamination. The vessels are refrigerated (in the range of 20-80 ^oF) to decrease the possibility of polymerization and control the heat of any other reactions, which might occur (3). The ethylene oxide can also be stored longer with refrigeration. The storage tanks are electrically grounded, placed in an area free from possible fires, and equipped with pressure relief valves (12).

Vent Gas Scrubber

Vent gas scrubber systems are commonly used to remove ethylene oxide from the stream. The scrubber column will be filled with pall ring packings. The ethylene oxide is absorbed by a strong acidic stream running countercurrent to the vent gas. Although a base can also be used, it is not as effective as the acid (3). The scrubbed gas is then released atmospherically and the absorbed ethylene oxide disposed of according to environmental regulations.

Prevention of Backflow

In order to prevent the possibility of backflow from downstream processes using ethylene oxide to the storage units, a detailed analysis is made of the piping system and vessels. Based on the distance between units and other structures, check valves are placed along the pipelines, particularly at the discharge site of pumps. In the event of an incident, the system can be shut off completely at specific spots, so as to avoid further backflow into the storage units, which could lead to exothermic reactions and possible vessel explosions.

Operability

With all of the above safety considerations in mind during the design phase, the process is easily operable. There are provisions for the system in the case of shutdown, plugs in the piping system, long-term breakdown of hardware, safer storage options, and a viable transportation plan. In the case of a spill or leak, the possible harmful effects are evaluated and determined to be relatively acceptable, in consideration of the societal benefits of ethylene oxide.

Economics:

The cost analysis of this proposal uses an operating life of 15 years, an operating year of 8000 hours, and a 15% discount factor for the profit projections. To make it easier to compare the numbers at a glance, most of the final values are rounded to three significant figures.

Cap Cost generates an estimate of the base cost and bare module cost of the design hardware. The cost includes the expense of a spare duplicate part for most of the equipment pieces. Due to storage limitations and expense, jEO generally includes only one spare for each equipment type. Table 6 lists the specific costs. Davis Corporation specifically requests that the preliminary cost analysis does not account for the absorption system.

Table 7 lists the electricity used by the pumps for an operating year of 8000 hours (14).

The breakdown of water costs is detailed in Table 8.

The reactor unit runs at a very high temperature, which boils off the cooling water. There is an option to either sell the steam for an additional profit, or reuse it for energy in a different section of the process.

Table 10 shows the amount and cost of catalyst.

Table 11 shows the wages paid to operators. Seader, et. al. recommend that 5 operators be present for each shift (14).

Total Cost Analysis

Table 12 lists the various costs of purchasing, installing, and operating the plant (14). Davis Corporation recommends neglecting the depreciation factor.

Table 13 lists the annual cash flows of the proposed design process. The projected construction period is 2 years, with a discount factor of 15%. With an operating life of 15 years and an operating year of 8000 hours, the necessary labor is calculated (14). The cash flow accounts for the 1% inflation rate of the price of ethylene oxide versus the 3% inflation rate of the reactants (6). As expected, the discounted cash flow value decreases steadily each year (see Figure 4). In addition to the expense of the reactants, the other costs of manufacturing, such as labor, operation overhead, utilities, and maintenance, are also subtracted from the annual sales revenue to arrive at the annual cash flow value. There is a profit of almost $48 million in the third year (see Table 13). This profit continues to grow to over $350 million in the last operating year. The final cumulative discounted cash flow continues to grow beyond $350 million in the last year (see Figure 5).

Conclusions:

In conclusion, jEO & Associates has determined that it is profitable to enter the EO market by constructing a plant that will come on-line in two years. jEO has developed the most profitable reactor train design possible. The process design focuses on a four-reactor train utilizing the typical Shell direct oxidation catalyst. The process produces

150,000 tons of EO per year. Considering mainly the reactor section of the process, the capital cost involved is $9.3 million, the yearly operating cost is $92 million, and the final cumulative discounted cash flow is $350 million. These results show that construction should begin immediately in order to start-up in two years.

References:

1. Anderlik, Jeff. Ceng 403 lecture, 9/22/99.

2. Bird, R.B., Stewart, W.E., and Lightfoot, E.N. Transport Phenomena, John Wiley and Sons, New York, 1960.

3. Celanese Web Site, Ethylene Oxide Users Guide, 10/2/99 http://www.hcc.com/eo/contents.html.

4. Coombs, Jonathan et al. JChem, Inc., 1997.

5. Gerhatz, Wolfgang, et. al. Ullman’s Encyclopedia of Industrial Chemistry, VCH, Germany, 1987, pp.117-135.

6. Goel, Ankur et al. ‘Say It Ain’t So, EO’ & Sons, 1999.

7. Kenson, Robert E. and Lapkin, M. "Kinetics and Mechanism of Ethylene Oxidation. Reactions of Ethylene and Ethylene Oxide on a Silver Catalyst" pp. 1493-1502.

8. Kiguchi, I., Kumazawa, T. and Nakai, T. "For EO: Air and oxygen equal," Hydrocarbon Processing, March 1976, pp.69-72.

9. Kim, Paul et. al. "Ethylene Oxide Reactor Design," 1998.

10. Kroschwitz, Jacqueline I. And Howe-Grant, Mary. Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, New York, 1994, pp. 915-951.

11. Levy, Guido and Piccinini, Norberto. "Ethylene Oxide Reactor: Safety According to Operability Analysis," Canadian Journal of Chemical Engineering, Volume 62, August 1984, pp. 547-558.

12. McKetta, John J. and Cunningham, William A. Encyclopedia of Chemical Processing and Design, Marcel Dekker, Inc., New York, 1983, Volume 20, pp. 282-303.

13. Ostadal, Kathryn, Personal correspondence.

14. Seader, J.D. et. al. Process Design Principles: Synthesis, Analysis, and Evaluation, John Wiley & Sons, New York, 1999.

15. Staff, "Markets & Economics/Product Focus: EO-EG," Chemical Week, June 3, 1998, p. 38.