Designing an Oxygen Purification Plant - Research Paper Example

Designing an oxygen purification plant Student’s Name College Instructor’s Name Course Name: Abstract Atmospheric air has mixture of gases with different boiling points as well as condensing points. Oxygen which is one mostly used constituent of air has a boiling point of 90K. Separation from atmospheric air and purification of oxygen is an important process where the air is liquidified to emanate any gas that is not required. Oxygen is obtained upon reaching 90K and this gives a minimum of 98% pure oxygen. The process that was used in the purification was Cryogenic Gas Liquefaction Systems to obtained 90%. Table of Contents Abstract 2 Introduction 4 The objective of the of project 4 Design of an oxygen purification plant 5 Working Principle 7 Estimated cost of the plant 8 Simulation and sensitivity analysis 8 Cost benefit analysis 12 Discussion 15 References 18 Introduction Several of gases comprising air have extensive industrial and commercial uses. Oxygen, nitrogen, neon, argon, krypton and xenon are these useful gases, and they are all produced by the fractional distillation of liquid air. Purified oxygen is basic requirement for human, plant and animal life. This oxygen is obtained from atmospheric environment industry process called Cryogenic Gas Liquefaction Systems where 0.9% of argon, 78% of nitrogen, and 0.04% of other gases are eliminated. Oxygen is the most important gas obtained from liquid air, with nitrogen ranking second (Essentialchemicalindustry, 2014). The major industrial use for oxygen is in the steel making industry, where it is used to burn off impurities in open-hearth or basic oxygen furnaces. Oxygen is also consumed by the chemical industry in the production of artificial atmospheres, for the oxidizing of rocket fuels, and for processing waste water. Nitrogen is also used in creating an inert atmosphere where the presence of oxygen might cause problems. It is also used as a refrigerant and for quick-freezing foods. Argon is another air-derived gas used to produce inert atmospheres (Dawson, Kalbassi, Siegmund and Thayer, 2010). In the welding of very active metals, for instance, nitrogen may be reactive and argon is used to protect the metal during welding. Argon is also used extensively to fill light bulbs. The major use for neon, krypton, and xenon is the filling of advertising signs, although new applications are being found, especially in the filed of lighting. It should be noted that helium is not recovered from the air but is obtained from natural gas wells where it makes up as much as 2% of the natural gas produced(Essentialchemicalindustry, 2014). The objective of the of project The objectives of the paper is to 1. Design a plant to produce oxygen at greater than 80%purity. 2. Draw the PFD for the process. 3. Calculation the resource usage associated with the operation of the process. 4. Vary the conditions to explore the effect of changes of the treatment plant efficiency. 5. To produce well-written scientific paper. Design of an oxygen purification plant The plant has three sections, the warm end process, cold box process and storage process, the warm end process has a container which compresses air, heats air through heat exchanger as well as receives air. This section receives air from the atmosphere the compresses it as well heats it. The cleaning process takes place this area as well as filtration. The container that is found in this area is called thermo-swing adsorbed(Dawson, Kalbassi, Siegmund and Thayer, 2010). Cold box process has a boiler, a column and heat exchanger. At this point impurities are eliminated. That is, gas which are able to cool below 90K and those that fail to cool after 90K(Essentialchemicalindustry, 2014). The liquid that is formed at 90K is collected and transported to the storage tank vowed in the oxygen storage system. The following is the diagrams of the system; Figure 1: oxygen purification plant (Golden, Taylor, Johnson, Malik and Raiswell, 2000) From the above diagram it can be noted that there is Warm end container which has heat exchanger, Compressor, Pre-filter, Air receiver and Air purification unit. The Coldbox has Boiler, main heat exchanger, expansion brake turbine and distillation column while oxygen storage consist of Vaporizer, liquid oxygen tank and filling station (Dawson, Kalbassi, Siegmund and Thayer, 2010). These systems can be operated and controlled by the microprocessors; the system can be easily programmed to suite the prevailing conditions. When the liquidified is insufficient, the powered activated heat exchanger is used to improve the temperature. This system is designed and drawn using Figure 2: Aspen design of gas-separation system Working Principle During purification, the plant contains cooling process, heat exchanger and storage. Before air can be liquefied, it is filtered to remove soot and other small dirt particles that would clog the equipment used later in the process. The air is compressed to five or six time’s normal atmospheric pressure and cooled. Some of the water and carbon dioxide solidify during the cooling process. The remainder of the water and carbon dioxide as well as impurities such as hydrocarbons is removed by a special filter(Dawson, Kalbassi, Siegmund and Thayer, 2010). The filtered air is then compressed to about 10MPa. As a result of being compressed, the temperature of the air rises. This energy is removed in a device called a heat exchanger. A heat exchanger consists of a series of tubes passing through a cylinder vessel(Dawson, Kalbassi, Siegmund and Thayer, 2010). One fluid passes through the tubes. Another cooler fluid flows through the vessel surrounding the tubes. Heat flows from the hotter fluid to the cooler fluid. The compressed air is cooled and then further compressed to about 15 MPA. Some of the cold gas is used to run one or more compressors. In the process of doing that work, the gas uses some of its internal energy. Thus, its temperature drops even more. Most of the cold, compressed gas is allowed to expand through a valve. A large part of the gas is liquefied through the Joule Thomson effect (Dawson, Kalbassi, Siegmund and Thayer, 2010). The liquid and extremely cold gases then enter a two stage distillation column. In the column the air is separated into high-purity nitrogen, oxygen, and other fractions. The high-purity products are sold and gas is used as a coolant in the heat exchangers. The other liquid fraction passes to a specialized distillation unit where neon, argon, krypton and Xenon are produced. During distillation, each component is removed at its boiling point (Dawson, Kalbassi, Siegmund and Thayer, 2010). Cold box has been the main mode of separation of the components of the plant. The initial separation takes place in a cold box separates the air mixture into portions having different boiling ranges. At the top of the coldbox, gases that were liquidified are removed (Dawson, Kalbassi, Siegmund and Thayer, 2010). These gases are principally the one-with low temperature. The oxygen is compressed in storage tank as liquefied gas. Estimated cost of the plant Simulation and sensitivity analysis The simulation was done under the following conditions Temperature - First temperature of heater exchanger is 5K to eliminate Helium, temperature towards the kettle 78 to eliminate nitrogen and Neon and in the kettle 91K for oxygen. The Ambient Temperature was assumed to be 298K Pressure- the atmospheric pressure was taken as 1atm, compression temperature was taken as 200atm while pressure in column was maintained at 1atm The molecular rate was at 180moles/sec while the Reflux Ratio was set at 6.8, and distillation to feed mole ratio was 0.925. The simulation worked using Peng-Robinson equation of state as Where R is gas constant, T is critical temperature, V is volume of gas, f is 0.46R2Tc2/pc, and g=0.08RTc/pc, Systematic Diagram Change in Atmospheric Conditions The results for the experiment are presented below; Flow of air into the plant occurs because of change in pressure like in displacement pumps where the gas already has some form of energy due to atmospheric pressure thus it is said to be primed. In the plant, the inlet and outlet lies at the same height and thus is connected to power which provides mechanical energy to the gas. The plant effectively changes from one energy level into another and this second form is responsible to make the air flow. The simple working principle of the plant involves power producing mechanical energy, the gas uses this energy and flows into the coldbox; which helps to increase the velocity or flow rate of the gas by cooling. In the moving fluid; mechanical energy gets transformed to kinetic energy because of which the pressure gets increased. This increased pressure coupled with the direction of movement of the of flow makes the gas go out through the outlet point (Gulich). Changing weather conditions cause variations of approximately 5% in the actual value of air pressure at seal level; 101.3kPa is only the average value. Air pressure also decreases with increasing elevation. The average air pressure in Leadville, Colorado, the highest incorporated city in the United States is 70kPa. Some Tibetans live at altitudes of over 5000m, where the average air pressure is only half its value at sea level. The figure below indicated that increases in pressure leads to high liquid fraction to a certain level. The increase started increasing at a decreasing rate at 200atm at a liquid fraction of 0.1638 When there is change in pressure, liquid fraction increases in same direction. The figure below shows that increase in temperature leads to decrease in liquid fraction ration. Therefore that value temperature is has the same trend as compressor exit temperature throughout. When it is at climax the same is observed that is at 500s. The figure indicates that the increase in temperature will lead to decreased in liquid fraction in the expansion valves. This is where cooling takes lace and reduction in temperature will definitely increase temperature. The inlet temperature and pressure have the same trend which is similar to trend taken by gas purify. This mean means that the inlet temperature and inlet temperature depends on each other. As the inlet temperature increases the inlet pressure increases. The temperature at coldbox and pressure, which shows what was expected that is they should show similar trend over change of time. Molecular flow vs. liquid fraction Looking at molar fluoride the graph shows a uniform liquid fraction which is a clear indication that the molar fluoride does not in any way affect the liquid fraction. Energy usage While evaluating varied values or performance characteristics of plant, we compared energy usage. When power is increased efficiency reduces due to conversion. Each plant has varied and different operating characteristics which are studied with the help of characteristic curves of these variables. In any gas to cool or expand kinetic energy is used. From graph based on power absorbance of 700MW and power emitted of 703MW. From this observation it is true that some extra heat could have been rising from the systems’ surrounding, variation of these flow rates gave different temperature values upon which determinations of the overall efficiency is possible. (Ventura and Risegari, 2008). In this case it is clear that there was some energy leased of emitted energy, since not all of was absorbed that’s why the efficiency was lower than 100%. Cost benefit analysis Benefits related to the building of the oxygen plant have now become close to and synonymous with the advantages associated with having the plant that uses the oxygen. The advantages of building oxygen plant can be recognized from two perspectives; the quality of life benefits and the economic development benefits. The benefits of economic development can be measured in terms of changes in the economic results such as incomes, jobs and profits. Benefits relating to quality of life can be considered in terms of intangible social advantages that affect how the community and environmentalist looks at project, the pattern in which community members behave and the contentment derived by community members. Economic benefits primarily relate to profits derived by owners of the plant because owners save a lot of money when they are not required to fund the corporate social responsibility issues. The new plant will create new jobs and enhanced incomes. Extra jobs will be created in constructing the plant, in operating the plant after it is completed and in other related businesses. There will be a jump in the number of restaurants and hotels that start operating from the vicinity of the plant and those that are already there will have a significant jump in the number of customers that visit them. Personal income levels of the community will also increase with the increase in the number of available jobs. Tax revenues in terms of sales tax and income tax collections will shoot up because of the enhanced spending patterns near the area of the plant as also because of the higher personal incomes (Katell and Wellman, 1960). The tangible and intangible advantages associated with oxygen plant are usually accompanied with both economic costs and quality of life costs. The biggest issue in this regard concerns whether the returns on investments made on the plant are more than the returns if the same investments were made in other areas. Most the company will ascertain the economic benefits that will accrue to a particular city or metropolitan area. Such studies are able to ascertain the concrete benefits resulting from building oxygen plant by way of the number of jobs that will be created, profits to be made and the amount of growth in revenues that will result from the construction and operation of the developed plant. The research material that is available in this regard is clearly indicative of the fact that there is not much economic benefit and growth from the development of oxygen plants. Some areas of experiential economic studies have offered the same conclusions although autonomous efforts in researching the economic effects of such plants have consistently concluded that there is no significant statistical relationship amongst the construction of plant and economic growth(National Renewable Energy Laboratory, 2006). To carry cost-benefit analysis quantitatively, the use of net present value (NPV) of costs. The net present value method enable us estimate lowest loss among the options by comparing its present value (PV) options. This is achieved by discounting costs to their present value using an interest rate of i = 10%; the management picks the option with the lowest PV (National Renewable Energy Laboratory, 2006). The PV method will provide information based on forecasts for the future of the project, enabling the management to estimate the net financial loss expected from such option. Let us assume the following Control Panel              Increased sales   10,000,000   Discount Rate  10%   Maintenance  15%   Cold box   2,500,000 Year 0 1 2 3 4 5 Initial Costs             Warm end container (1,500,000)           Oxygen storage (1,750,000)           Cold box (2,500,000)           Recurring Costs             Maintenance   (225,000) (225,000) (225,000) (225,000) (225,000) Salaries   (262,500) (262,500) (262,500) (262,500) (262,500) Electricity   (20,000) (20,000) (20,000) (20,000) (20,000) Stationary   (62,500) (62,500) (62,500) (62,500) (62,500) Total Costs (5,750,000) (570,000) (570,000) (570,000) (570,000) (570,000)               Initial Benefits                           Recurring Benefits             Increase Profit   4,000,000 4,000,000 4,000,000 4,000,000 4,000,000 Environment cost saving   (60,000) (60,000) (60,000) (60,000) (60,000) Deprecation tax shiled   18,000 18,000 18,000 18,000 18,000 Total Benefits - 3,958,000 3,958,000 3,958,000 3,958,000 3,958,000               Net Cash Flow (5,750,000) 3,388,000 3,388,000 3,388,000 3,388,000 3,388,000 NPV 4,382,194 2,823,333 2,352,778 1,960,648 1,633,873 1,361,561 The project generates positive net present values thus the plant should be constructed. Discussion From the results it is a clear that temperature and pressure are critical variables that affect the purification process. The purification process however is also affected as indicated in the equation in simulation above. This means our plant performs well as we increase the temperature and the atmospheric pressure. However, the atmospheric pressure changes to a certain level where a liquid fraction remains constant. We know, in order to maintain a temperature and pressure of a desired volume of air is necessary for the plant can work efficiently (Dawson, Kalbassi, Siegmund and Thayer, 2010). These optimal results can be achieved when the optimal variables are used by he plant. From this observation it is true that there were extra heat gained from the environment. Environmental conditions could have been the source of this extra heat gain because the plant has a mechanism that can enable it to either gain or lose heat to the adjacent environment. Within the same experimental set up, variation of flow rates gave liquid fraction values upon which calculation of the overall efficiency could be done together with performance of energy balance across the heat plant. These results would naturally be different for different gases seeing as they will have different molecular masses. The underlying principles of separation remain the same however. The temperature will determine the end results (). The temperature can be set at 91K if the operator wants to hasten reaction and lower the temperature if he wants to slow down the reaction time. The exact temperature needed would be dictated by the substances involved. The concentration of the reactants within the reaction tank would also be taken into consideration and calculated for their morality in order to determine their initial concentration and then compare it with the conductivity data to determine the level of reaction that has taken place. A pre-calculation of the moles needed to suitably react to each other should have been calculated beforehand in order to achieve the best results as possible The plant designed will have the ability to manufacture oxygen using three stages, cleaning the air, liquefying and distillation of liquid air. The plant will begin by removing impurities through a filtering process then it will be cooled down to a level where moist water gas will be condensed and removed. Then it will pass through zeolite to remove carbon dioxide. At this stage we will have pure air which will pass through the pipe shown for liquefying. Liquefying air will be done and some of the elements of air will be eliminated. The following is the boiling points of various constituents of air and they will be removed once a certain boiling temperature is reached (Golden, Taylor, Johnson, Malik and Raiswell, 2000). Once the gas is cooled to their boiling point, it is liquefied it is removed, for example helium will be removed at 4K, nitrogen at 77K while oxygen at 90K. This means that any substance that is cooled below 89 is eliminated as a impurities. At this point we remain with oxygen and other gases, then at 90 it is liquefied and anything that is not liquefied at 90 is eliminated as impurity(Essentialchemicalindustry, 2014). This will give over 90% pure oxygen, at this point any gas that reaches a cooling point will be distilled therefore the importance of distillation section comes into play (Essentialchemicalindustry, 2014). We know, in order to maintain a desired flow rate of a desired volume of gases, it is necessary that the plant air receiver to a definite total pressure value. This equilibrium can be achieved when the total dynamic pressure produced by the air receiver unit becomes equal to that desired. This equilibrium position is hard to achieve as their always remains a difference among the two ends owing to the mechanical and personnel errors in plant management. Considering the efficiency and power usage curve, first increases and then after a point, it starts decreasing. This happens because calculation of efficiency includes power by the mechanical power. First, when the mechanical power remains below the plant power the efficiency increases. But as time passes, the plant power increases and exceeds the supplied power value and thus the efficiency starts decreasing. Thus, the curve first shows a rise and then a decline. The value of flow rate at which the efficiency is highest or the value one step less than the point at which the efficiency starts falling is the peak value and corresponding most productive flow rate of the plant. CONCLUSIONS The design and simulation of air liquefaction under Cryogenic Gas Liquefaction Systems done using Aspen Plus simulating tool. There was variation of atm and temperature and result showed that increase in lead to increase lead to increase in liquid fraction while increase in molecular flow lead to the same liquid fraction. This meant that liquid fraction is not influenced by the flow rate. References Dawson, B., Kalbassi, M., Siegmund, S. & Thayer, M. (2010). Optimizing Oxygen Plant Performance: Improving Production and Reliability of Existing Plants While Reducing Costs, Air Products & Chemicals, Inc. Essentialchemicalindustry, (2014). The essential chemical industry: oxygen, nitrogen and air gases Golden, T., Taylor, F., Johnson, L., Malik, N. & Raiswell, C., (2000). Purification of Air. Golden, T., Taylor, F., Malik, N., Raiswell, C. & Salter, E., (2003). "Process for Reducing the Level of Carbon Dioxide in a Gaseous Mixture",. Katell, S. & Wellman, P., 1960. Cost of tonnage oxygen: An evaluation of tonnage oxygen Plants. Ltd, D. e. (2007) an introduction to high performance CCC for sample purification. National Renewable Energy Laboratory (2006). Equipment Design and Cost Estimation for Small Modular Biomass Systems, Synthesis Gas Cleanup, and Oxygen Separation Equipment Richard, T., S., Penoncello & Eric, W., (2012). Thermodynamic Properties of Cryogenic Fluid Plenum Press. Ventura, G. & Risegari, L.,2008. The Art of Cryogenics, Low-temperature experimental Elsevier Read More