Summary This chapter contains about fertilizer and its types, ammonia with its history and its expansion in industry along with the physical and chemical properties, uses and world data of ammonia production. The capacity of ammonia plant in the major industries of world and those of the plants located in Pakistan is presented in the tables. The basic principle of simulation and modeling is discussed. A brief history of simulation and list of different simulators that are used in industries is given in the chapter. The advantages and uses of ChemCAD are discussed in detail. Ammonia Ammonia is an intermediate product in the manufacture of nitrogenous fertilizers. It is also used for direct application to the soil and in aqua condition with solutions of other nitrogenous fertilizers like ammonium nitrate and/or urea. Besides these, ammonia finds application in the production of nitric acid, soda ash, cleaning agents, leather tanning, petroleum refining, pulp & paper industry, textiles, refrigeration, rubber & synthetic resin industries, explosives and food and beverage industries [1]. 1.1 History of Ammonia The catalytic synthesis of ammonia from its elements is one of the greatest achievements of industrial chemistry. This process not only solved a fundamental problem in securing our food supply by production of fertilizers but also opened a new phase of industrial chemistry by laying the foundations for subsequent high-pressure processes like methanol synthesis, oxo synthesis, Fischer-Tropsch Process, coal liquefaction, and Reppe reactions. Continuous ammonia production with high space yields on large scale combined with the ammonia oxidation process for nitric acid, which was developed immediately after ammonia synthesis, enabled the chemical industry for the first time to compete successfully against a cheap natural bulk product, namely, sodium nitrate imported from Chile. The driving force in the search for methods of nitrogen fixation, of course, was to produce fertilizers. In principle there are three ways of breaking the bond of the nitrogen molecule and fixing the element in a compound as follows [1]: To combine the atmospheric elements nitrogen and oxygen directly to form nitric oxides. To combine nitrogen and hydrogen to give ammonia. To use compounds capable of fixing nitrogen in their structure under certain reaction conditions. A vast amount of research in all three directions led to commercial processes for each of them: the electric arc process, the Cyanamid process and ammonia synthesis, which finally displaced the other two and rendered them obsolete. The availability of cheap hydroelectric power in Norway and the United States stimulated the development of the electric arc process. Air was passed through an electric arc which raised its temperature to 3000 °C, where nitrogen and oxygen combine to give nitric oxide. In 1904 Christian Birkeland performed successful experiments and, together with Sam, Eyde, an industrial process was developed and a commercial plant was built, which by 1908 was already producing 7000 ton of fixed nitrogen. Working in parallel, Schoenherr at BASF developed a different electric arc furnace in 1905. The Norwegians and BASF combined forces in 1912 to build a new commercial plant in Norway. However, since at this time pilot-plant operation of ammonia synthesis was already successful, BASF withdrew from this joint venture soon after. Nevertheless, the Norwegian plants operated throughout World War I and had total production of 28000T/A of fixed nitrogen with a power consumption of 210,000kW.The specific energy consumption was tremendous: 60000kW per ton of fixed nitrogen. Had this electricity been generated from fossil fuels this figure would correspond to about 600GJ per ton nitrogen, which is about 17 times the consumption of an advanced steam-reforming ammonia plant in 1996 [1]. The Cyanamid process developed by FRANK and CARO in 1898, was commercially established by 1910. Calcium carbide, formed from coke and lime in a carbide furnace (Calcium Carbide), reacts with nitrogen to give calcium Cyanamid, which can be decomposed with water to yield ammonia. The process was energetically very inefficient, consuming 190GJ per ton of ammonia. Some other routes via barium cyanide produced from barytes, coke and nitrogen, or using the formation of titanium nitride were investigated in Ludwigshafen by Bosch and Mittasch but did not appear promising. In 1934, 11 % of world nitrogen production (about 2 × 106T/A), was still based on the Cyanamid process, and some plants even continued to operate after World War II [1-5]. After Berthollet proved in 1784 that ammonia consists of nitrogen and hydrogen and was also able to establish the approximate ratio between these elements, many experiments in the 1800s were aimed at its direct synthesis, remained unsuccessful, One of the reasons for the lack of success was the limited knowledge of thermodynamics and the incomplete understanding of the law of mass action and chemical equilibrium. It was the new science of physical chemistry, which developed rapidly in the late 1800s, that enabled chemists to investigate ammonia formation more systematically [6-8]. Around 1900 Fritz Haber began to investigate the ammonia equilibrium at atmospheric pressure and found minimal ammonia concentrations at around 1000°C (0.012 %). Apart from Haber, Ostwald and Nernst were also closely involved in the ammonia synthesis problem, but a series of mistakes and misunderstandings occurred during the research. For example, Ostwald withdrew a patent application for an iron ammonia synthesis catalyst because of an erroneous experiment; while Nernst concluded that commercial ammonia synthesis was not feasible in view of the low conversion he found when he first measured the equilibrium at 50 – 70bar [9-10]. After a controversy with Nernst, Haber repeated his measurements at atmospheric pressure and subsequently at higher pressures overcoming his colleague's preoccupation with the unfavorable equilibrium concentrations. Haber concluded that much higher pressures had to be employed and that, perhaps more importantly, a recycle process was necessary [10]. The amount of ammonia formed in a single pass of the synthesis gas over the catalyst is much too small to be of interest for an economic production. Haber therefore recycled the unconverted synthesis gas. After separating the ammonia by condensation under synthesis pressure and supplementing with fresh synthesis gas to make-up for the portion converted to ammonia, the gas was recirculated by means of a circulation compressor to the catalyst-containing reactor. Haber also anticipated the preheating of the synthesis gas to reaction temperature (at that time 600°C ) by heat exchange with the hot exhaust gas from the reactor, the temperature of which would be raised by the exothermic ammonia formation reaction sufficiently (about 18°C temperature rise for a 1 % increase of the ammonia concentration in converted synthesis gas) [10]. In 1908 Haber approached BASF (Badische Anilin & Soda Fabrik at that time) to seek support for his work and to discuss the possibilities for the realization of an industrial process. His successful demonstration in April 1909 of a small laboratory scale ammonia plant having all the features described above finally convinced the BASF representatives, and the company's board decided to pursue the technical development of the process with all available resources. In an unprecedented effort, Carl Bosch, together with a team of dedicated and highly skilled co-workers, succeeded in developing a commercial process in less than five years. The first plant started production at Oppau in September 1913 and had a daily capacity of 30 ton of ammonia. Expansions increased the capacity to about 250T/D in 1916/17 and a second plant with a capacity of 36,000T/A went on stream in 1917 in Leuna. Further stepwise expansions, finally reaching 240,000T/A, already decided in 1916, came in full production only after World War I. After World War I ammonia plants were built in England, France, Italy, and many other countries based on a BASF license or own process developments, with modified process parameters, but using the same catalyst [10]. Up to the end of World War II, plant capacities were expanded by installing parallel lines of 70 – 120T/D units, and synthesis-gas generation continued to be based on coal until the 1950s. With growing availability of cheap petrochemical feedstock and novel cost-saving gasification processes (steam reforming and partial oxidation) a new age dawned in the ammonia industry. The development started in the USA, where steam reforming of natural gas was used for synthesis gas production. This process was originally developed by BASF and greatly improved by ICI, who extended it to naphtha feedstock. Before natural gas became available in large quantities in Europe, partial oxidation of heavy oil fractions was used in several plants. The next revolution in the ammonia industry was the advent of the single-train steam reforming ammonia plants, pioneered by M. W. Kellogg and others. The design philosophy was to use a single-train for large capacities (no parallel lines) and to be as far as possible energetically self-sufficient (no energy import) by having a high degree of energy integration (process steps in surplus supplying those in deficit). Only through this innovative plant concept with its drastic reduction in feedstock consumption and investment costs, could the enormous increase in world capacity in the following years became possible. Increasing competition and rising feedstock prices in the 1970s and 1980s forced industry and engineering companies to improve the processes further [10]. The LCA process of ICI and the KRES/KAAP process, which is the first process since 1913 to use a non-iron synthesis catalyst, are recent advances that make a radical breakaway from established technology [16-18]. 1.2 History of Ammonia in Pakistan History of manufacture of Ammonia in Pakistan is not so ancient. At the time of independence, there was no ammonia industry in Pakistan. The trend of ammonia industry was developed with the use of fertilizer. The start of fertilizer/ammonia industry was taken up in after 1960's during the rule of Field Marshal Ayyub Khan. Afterwards many fertilizer industries were set up in Pakistan in private as well as public sector. Now National Fertilizer Corporation of Pakistan is making its best efforts for the prosperity. Since 1954 the .following sweeping changing in the technology of ammonia manufacture has taken place [33]. Feeds ranging from natural gas to naphtha have been processed by steam – hydrocarbon reforming at pressure up to 500 lb/in2 gauge. Electric power consumption has been reduced to practically zero due primarily to the use of a highly efficient energy cycle which incorporates high pressure steam generation in conjunction with the maximum use of turbine drives tor pumps and centrifugal compressors. Enormous improvements in the gas purification processes. Several low utility process are available for CO2 removal including promoted MEA, promoted hot potassium carbonate process, sulfinol, the two stage tri ethanolamine/ mono ethanolamine system and others. Moreover, removal of residual CO has been enormously simplified by the use of the methanation system. Space requirements for the purification system have been minimized. Improved heat recovery, particularly in the reformer effluent system and the various catalyst reaction services. Efficient use of steam. Use of higher activity catalyst for all process services. 'the introduction of low temperature shift conversion catalyst has simplified the design of the raw gas generation system and permitted substantial reduction in the quantity of feed processed in the reformer because of the associated reduction in purge in the synthesis loop. Plant capacities have been increased from 600 to 1700 tons/ day as 100% single train operations throughout the unit including the ammonia convertor. In addition, there have been significant improvements in the fabrication of ammonia converters. Full closure converters can be offered in a wide range of capacities and operating pressures. Moreover, the internal layout of ammonia converters have been modified in the direction of low pressure drop which still retaining efficient distribution of gas through the catalyst beds. The number of catalyst beds for the quench–type converter has been optimized. Reduced both the volume of catalyst and the converter size by 10 –25% depending on the size of catalyst used and the available pressure drop of the loop. Improvement in compressor design for all process service. Centrifugal compressors–can be provided for the synthesis gas service for pressure up to 4700 lb/in2(g) for size in excess of 1700 tons/day operating over a wide range of speeds and horsepower. Development of improved method for feed desulphurization including hydrodesulphurization of naphtha feeds. Improvements in both cobalt molybdenum catalyst and zinc oxide sulfur absorbent catalyst have enabled all feeds to be desulfurized to levels of less than 0.25ppm sulfur, thus ensuring protection of reforming catalyst against sulfur poisons with a resultant long catalyst life. 1.3 Expansion in Industry Major expansion of the ammonia industry began in 1963. The demand for Nitrogen based fertilizer throughout the world and the prospects for increased consumption in future years stimulate fertilizer producers to build many new ammonia plants. During the last 8 years, a trend has developed towards building large scale single train plants with capacities of 600 to 1500 tons per day. During the last quarter century many improvements have been made in the technology and design of ammonia plants. Significant improvements have been made in plant equipment, catalysts and instrumentation. These developments have contributed to substantiate reduction in the capital cost and operation costs of Ammonia plants. In 1960, the world production of ammonia was about 13 million ton. The use of ammonia can he apprehended by the fact that in 1967, 12 million of ammonia was manufactured in United States of America raised to 18 million tons the very next year [33]. Major development of ammonia began in 1963, so that ammonia requirement for the fertilizer industry can be fulfilled. During the last quarter century many improvement have been made in plant design technology. Significant improvements have been made in plant equipment catalyst and instrumentation. These developments have caused substantiate reduction in capital cost and operation costs of ammonia plants. Research work is still carried on for further improvements [33]. 1.4 Improvement in NH3 Production process These improvements as follows [33]: 1940 to 1952 Main features Capacity was150T/D CO2 Removal by Water wash, 20% MEA No. of NH3 converter which is using is 3 Process characteristics Low pressure catalyst reforming of natural gas i.e. (0.6-1.0) kg/cm2 Low pressure efficiency High power consumption. 1953 Main features Capacity was 160 T/D CO2 Removal by 20% MEA 2 Ammonia converters are using Process characteristics First increase in reforming i.e. 4.2 kg/cm2 Substantial reduction in power consumption Gas holder and associated operation eliminated 1955 Main features Capacity was 300T/D CO2 removal 20% MEA Hot K2CO3 Only one NH3 converter was used Process characteristics Further increase in reformer pressure i.e. 8.8kg/cm2 Reduction in Fuel & power consumption First use of centrifugal compression in raw synthesis gas service. Additional feeds processed include refinery gas and naphtha. Use of Hot K2CO3 for CO2 removal. 1960 to 1962 Main features Capacity increased up to 360T/D CO2 Removal about 20% MEA One NH3 converter is used. Process characteristics Further increase in reformer pressure i.e. (14.5-18.4)kg/cm2 Elimination of copper liquor system. Elimination of compression in raw gas. Use of high air pre-heat for secondary reformer. Internal main folding of reformer catalyst lube to reduce heat losses. Greater recovery of heat of reaction for all catalytic services. 1963 Main features Capacity was 320T/D CO2 removal was 20% MEA One NH3 converter is used. Process characteristics Further increase in reformer pressure i.e. (21-28.3)kg/cm2 High thermal efficiency, reduced fuel consumption. Introduction of improved low temperature co shift catalyst. Reduced purge rate in synthesis loop. 1964 Main features Capacity increase up to 600T/D CO2 Removal is same 20% MEA One NH3 converter is used. Process characteristics: First single train 600 ton ammonia plant. First use of centrifugal compressor to compress synthesis gas to 150atm. Approximately 80% of all compression horsepower (including air + Refrigeration) based on use of centrifugal machines. 1965 to 1972: Main features Capacity increase up to 600 to 1700T/D CO2 removal 20% MEA by using Vertrocoke, Catacarb, Carsol, Sulfinol, One NH3 converter is used Process characteristics Further increase in reformer pressure in conjunction with low pressure synthesis i.e. (31.7-33.5)kg/cm2. Entire synthesis gas compression (including recycling service) handled by a two stage centrifugal compressor for synthesis pressure up to 220atm. All compression services based on centrifugal compressors. Synthesis up to 320atm accommodated by centrifugal compressor (using three stage machines). High efficiency energy cycle in conjunction with more use of steam turbine for pump and compressors for high pressure steam generation. Low pressure consumption (especially zero to some design). Low feed and utility cost. High secondary reformer air pre-heat temperature, mild primary reformer condition despite increase in reformer pressure. First 1700 ton ammonia plant based on a single train operation. Improved low pressure drop ammonia convertor design [19]. 1.5 Physical Properties of Ammonia The NH3 molecule has a pyramidal structure of the type shown in the diagram below, in which the nitrogen atom has achieved as table electronic configuration by forming three electron pair bonds with the three hydrogen atoms. The H-N-H bond angle in the pyramid is 106.75˚, which is best explained as resulting from the use of sp3 hybrid bonding orbitals by the nitrogen atom. This should yield tetrahedral bond angles with the result that one sp3 orbital is occupied by the unshared pair of electrons. The repulsive effect of this unshared pair, which is concentrated relatively near to the nitrogen nucleus on the shared pairs of electrons forming the N-H bonds, produces a slight compression of the HNH bond angles, thus accounting for the fact that they are slightly less than tetrahedral (109.5°) [19]. The dipole moment of the ammonia molecule, 1.5Debyes, is a resultant of the combined polarities of the three N-H bonds and of the unshared electron pair in the highly directional sp3 orbital. The pyramidal ammonia molecule turns inside out readily, and it oscillates between the two extreme positions at the precisely determined frequency of 2.387013 × 1010 Hz. This property has been used in the highly accurate time-measuring device known as the ammonia clock [19]. Anhydrous (water-free) ammonia gas is easily liquefied under pressure (at 20 °C liquid ammonia has a vapor pressure of about 120lb per sq. in.) It is extremely soluble in water; one volume of water dissolves about 1,200 volumes of the gas at 0°C (90grams of ammonia in 100cc of water), but only about 700 volumes at room temperature and still less at higher temperatures. The solution is alkaline because much of the dissolved ammonia reacts with water, H2O, to form ammonium hydroxide, NH4OH, a weak base [19]. Liquid ammonia is used in the chemical laboratory as a solvent. It is a better solvent for ionic and polar compounds than ethanol, but not as good as water; it is a better solvent for nonpolar covalent compounds than water, but not as good as ethanol. It dissolves alkali metals and barium, calcium, and strontium by forming an unstable blue solution containing the metal ion and free electrons that slowly decomposes, releasing hydrogen and forming the metal amide. Compared to water, liquid ammonia is less likely to release protons (H+ ions), is more likely to take up protons (to form NH4+ ions), and is a stronger reducing agent. Because strong acids react with it, it does not allow strongly acidic solutions, but it dissolves many alkalis to form strongly basic solutions [19]. The principle physical constants for ammonia are summarized in Table 1.1. Ammonia is highly mobile in the liquid state and has a high thermal coefficient of expansion [19]. Table 1.1 The principle physical constants for ammonia [19] Property Value or Detail Molecular Mass 17.03 g/mol Color Colorless Odor Sharp, Irritating Physical State Gas (at room temperature) Melting Point -77.71oC Boiling point -33.43oC Flash Point 11oC Decomposition Point 500 oC Density(Gas) 0.7714 g/L Density(Liquid) 0.6386 g/L Critical Density 0.35g/L Critical Temperature 132.4oC Critical Pressure 11.28MPa Heat Of Fusion 332.3kJ/kg Heat Of Vaporization 1370kJ/kg Standard Enthalpy of formation -46.22kJ/mol 1.6 Chemical Properties of Ammonia Ammonia is an excellent solvent for salts, and has an exceptional capacity to ionize electrolytes. The alkali metals and alkaline earth metals (except beryl-lium) are readily soluble in ammonia. Iodine, sulfur, and phosphorus dissolve in ammonia. In the presence of oxygen, copper is readily attacked by ammonia. Potassium, silver, and uranium are only slightly soluble. Both ammonium and beryllium chloride are very soluble, whereas most other metallic chlorides are slightly soluble or insoluble. Bromides are in general more soluble in ammonia than chlorides, and most of the iodides are more or less soluble. Oxides, fluorides, hydroxides, sulfates, sulfites, and carbonates are insoluble. Nitrates (e.g., ammo-nium nitrate) and urea are soluble in both anhydrous and aqueous ammonia making the production of certain types of fertilizer nitrogen solutions possible. Many organic compounds such as amines (qv), nitro compounds, and aromatic sulfonic acids, also dissolve in liquid ammonia. Ammonia is superior to water in solvating organic compounds such as benzene (qv), carbon tetrachloride, and hexane [20]. Table 1.2 Chemical behavior of ammonia [20] Property Value or Details Chemical Formula NH3 Type of Base Weak Affinity(Water) High Corrosiveness Corrosive to Some Metals Oxidation Power Strong Reducing Agent Reactivity Quite Reactive Volatility Increases with increases in pH 1.7 General Raw Materials for Ammonia Production The basic raw material for ammonia is nitrogen and hydrogen. Nitrogen is invariably obtained from air as far as hydrogen is concerned careful consideration must be given to the choice of raw material and process of its projection. NH3, plant operation costs are already directly influenced by the cost of hydrogen production. Different raw materials are given below: Natural gas Naphtha Heavy fuel oil Coat and Lignite Liquefied petroleum gas Electrolytic hydrogen By product hydrogen [20]. 1.8 Raw Material Available in Pakistan The best raw material used in the manufacturing of NH3, is natural gas. However, following materials are available but not in use as on commercial basis [34]. Naphtha Only 20% of the total demand of fuel oil is met with from the industry. The test is imported so it is not considerably as raw material for NH3. Coal Coal is available in Pakistan at Makerwal, Dhodak and Kalabagh but it quality is very poor and reserves are not sufficient to meet the needs. Electricity Electricity is the general demand of any country. Here in Pakistan it is expensive and hence can't be used as a raw material. By-Product Hydrogen It is not available and sufficient quality is not available in sufficient quantity so as to prove economical for NH3. Natural Gas Natural gas is the only most convenient and economical raw material available for NH3 in Pakistan. 1.9 Uses of Ammonia Figure 1.1 Percentage usage of ammonia [20] In Fertilizer Approximately 83% (as of 2003) of ammonia is used as fertilizers either as its salts or as solutions. Consuming more than 1% of all man-made power, the production of ammonia is a significant component of the world energy budget [20]. Precursor to nitrogenous compounds Ammonia is directly or indirectly the precursor to most nitrogen-containing compounds. Virtually all synthetic nitrogen compounds are derived from ammonia. An important derivative is nitric acid. This key material is generated via the Ostwald process by oxidation of ammonia with air over a platinum catalyst at 700–850°C, ~9 atm. Nitric oxide is an intermediate in this conversion. NH3 + 2 O2 → HNO3 + H2O Nitric acid is used for the production of fertilizers, explosives, and many organic nitrogen compounds [20]. In Cleaner Household ammonia is a solution of NH3 in water (i.e., ammonium hydroxide) used as a general purpose cleaner for many surfaces. Because ammonia results in a relatively streak-free shine, one of its most common uses is to clean glass, porcelain and stainless steel. It is also frequently used for cleaning ovens and soaking items to loosen baked-on grime. Household ammonia ranges in concentration from 5 to 10 weight percent ammonia [21]. Refrigeration Because of its favorable vaporization properties, ammonia is an attractive refrigerant. It was commonly used prior to the popularization of chlorofluorocarbons (Freon’s). Anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks because of its high energy and low cost. The Kalina cycle, which is of growing importance to geothermal power plants, depends on the wide boiling range of the ammonia-water mixture. Ammonia is used less frequently in commercial applications, such as in grocery store freezer cases and refrigerated displays due to its toxicity [22]. For remediation of gaseous emissions Ammonia is used to scrub SO2 from the burning of fossil fuels, and the resulting product is converted to ammonium sulfate for use as fertilizer. Ammonia neutralizes the nitrogen oxides (NOx) pollutants emitted by diesel engines. This technology, called SCR (selective catalytic reduction), relies on a vanadium-based catalyst [23]. As a fuel Ammonia was used during World War II to power buses in Belgium, and in engine and solar energy applications prior to 1900. Liquid ammonia was used as the fuel of the rocket airplane, the X-15. Although not as powerful as other fuels, it left no soot in the reusable rocket engine and its density approximately matches the density of the oxidizer, liquid oxygen, which simplified the aircraft's design [23]. Ammonia has been proposed as a practical alternative to fossil fuel for internal combustion engines. The calorific value of ammonia is 22.5MJ/kg (9690Btu/lb) which is about half that of diesel. In a normal engine, in which the water vapor is not condensed, the calorific value of ammonia will be about 21% less than this figure. It can be used in existing engines with only minor modifications to carburetors/injectors [23]. To meet these demands, significant capital would be required to increase present production levels. Although the second most produced chemical, the scale of ammonia production is a small fraction of world petroleum usage. It could be manufactured from renewable energy sources, as well as coal or nuclear power. It is however significantly less efficient than batteries. The 60MW Rjukan dam in Telemark, Norway produced ammonia via electrolysis of water for many years from 1913 producing fertilizer for much of Europe. If produced from coal, the CO2 can be readily sequestrated (the combustion products are nitrogen and water). In 1981 a Canadian company converted a 1981 Chevrolet Impala to operate using ammonia as fuel [23]. Ammonia engines or ammonia motors, using ammonia as a working fluid, have been proposed and occasionally used. The principle is similar to that used in a fireless locomotive, but with ammonia as the working fluid, instead of steam or compressed air. Ammonia engines were used experimentally in the 19th century by Goldsworthy Gurney in the UK and in streetcars in New Orleans in the USA [23]. As antimicrobial agent for food products As early as in 1895 it was known that ammonia was "strongly antiseptic. It requires 1.4 grams per liter to preserve beef tea. Anhydrous ammonia has been shown effective as an antimicrobial agent for animal feed and is currently used commercially to reduce or eliminate microbial contamination of beef.  The New York Times reported in October, 2009 on an American company, Beef Products Inc., which turns fatty beef trimmings, averaging between 50 and 70 percent fat, into seven million pounds per week of lean finely textured beef by removing the fat using heat and centrifugation, then disinfecting the lean product with ammonia; the process was rated by the US Department of Agriculture as effective and safe on the basis of a study (financed by Beef Products) which found that the treatment reduces E. coli to undetectable levels [23]. As a stimulant in sports Ammonia has found significant use in various sports – particularly the strength sports of power lifting and Olympic weightlifting as a respiratory stimulant (psychoactive drugs) [23]. Textile Liquid ammonia is used for treatment of cotton materials, give properties like Mercerization (It is a treatment for cotton fabric and thread that gives fabric or yarns a lustrous appearance and strengthens them using alkalies). In particular, it is used for pre-washing of wool [23]. Lifting gas At standard temperature and pressure ammonia is lighter than air, and has approximately 60% of the lifting power of hydrogen or helium. Ammonia has sometimes been used to fill weather balloons as a lifting gas. Because of its relatively high boiling point (compared to helium and hydrogen), ammonia could potentially be refrigerated and liquefied aboard an airship to reduce lift and add ballast (and returned to a gas to add lift and reduce ballast) [23] Wood working Ammonia was historically used to darken quarter sawn white oak in Arts & Crafts and Mission style furniture. Ammonia fumes react with the natural tannins in the wood and cause it to change colors [23]. 1.10Literature Survey 1.10.1Ammonia in Pakistan Pakistan is an agricultural country where about 72% of the total population not only resides in rural areas but also relies for its sustenance on Agri-activities. This sector is contributing a lion's share in the national economy. Most of the national economic target is dependent on the performance of our agricultural sector; It contributes 24% to the; total GDP. Cotton, Rice, Sugarcane and Wheat are major crops having economics importance. The fertilizer is an important input, which boosts the Agri-production. Unfortunately, it is used three times lower in our country than that of the developed countries in the world. We are not still self-sufficient in producing our staple food grain, soil deterioration, nutrient mining. And there is insufficient and inadequate use of fertilizer. The industries that produce ammonia in Pakistan are listed below [33]: Pak Arab fertilizer ltd. Multan Fauji fertilizer ltd. Goth Macchi. Pak Saudi Fertilizers (Now FFC) Ltd. Mirpur Mathelo. Pak American (Agritech) Ltd. Daudkhel Engro Chemicals ltd. Dharki. Dawood Hercules Ltd. Lahore. 1.10.2 Ammonia Production in Pakistan Table 1.3 Ammonia productions in Pakistan [33] INDUSTRIES AMMONIA CAPACITY (MTPA) PakArab fertilizer ltd.(Pfl) Multan 316,800 FFC (Goth Macchi). 403,000 FFC (Mirpur Mathelo) 413,000 Pak American (Agritech) Ltd. Daudkhel 237,250 Engro Chemicals ltd. Dharki 268,000 Dawood Hercules Ltd. Lahore. 310,250 In the next 10 years there will be a shortage of urea in Pakistan, which is the critical situation for those who are linked with the agricultural field; therefore more plants of urea are required to overcome this difficulty. From the table we can see that Ammonia is the 2nd most used chemical in the world. So we can say there is a bright future for Ammonia Production plant. Total Annual Production Capacity Available = 4,421,340 MT Use of Ammonia in Fertilizer Total Annual Produced Ammonia is used to make following [20]: Urea = 6,349,200 MT NP =735,900 MT DAP =676,500 MT CAN =798,600 MT About 12000-15000 MT Anhydrous Ammonia is also required to be used in Non-Fertilizer Industries [20]. 1.10.3 World Wide Ammonia production Ammonia production increases at an annual growth rate of 2-3%, with China leading global production and capacity surplus. Growth in ammonia production is directly related to the demand for phosphate and nitrogen fertilizers, as nearly 90% of ammonia and ammonium derivatives are applied in mineral fertilizer production worldwide. The trio of China, US and Morocco are considered market leaders in the production of ammonium phosphate worldwide [23]. Largest Ammonia producing Countries Largest Ammonia producing countries may include following countries: USA China Russia India Middle East Countries. Figure 1.4 Following Graph shows the Changing trend of Ammonia Production in Million Metric Tons since 1991 to 2012 in above countries [23] 1.11 Simulation Process simulation is used for the design, development, analysis, and optimization of technical processes such as: chemical plants, chemical processes, environmental systems, power stations, complex manufacturing operations, biological processes, and similar technical functions. The Word simulation is derived from the Latin word simulare which means pretend. Simulation is thus an inexpensive and safe way to experiment with the system model. However, the simulation results depend entirely on the quality of the system model. It is a powerful technique for solving a wide variety of problems [25]. 1.12 Main Principle Process simulation is a model-based representation of chemical, physical, biological, and other technical processes and unit operations in software. Basic prerequisites are a thorough knowledge of chemical and physical properties of pure components and mixtures, of reactions, and of mathematical models which, in combination, allow the calculation of a process in computers. Process simulation software describes processes in flow diagrams where unit operations are positioned and connected by product or product streams. The software has to solve the mass and energy balance to find a stable operating point. The goal of a process simulation is to find optimal conditions for an examined process. This is essentially an optimization problem which has to be solved in an iterative process. Process simulation always uses models which introduce approximations and assumptions but allow the description of a property over a wide range of temperatures and pressures which might not be covered by real data. Models also allow interpolation and extrapolation - within certain limits - and enable the search for conditions outside the range of known properties [25]. 1.13 Modeling The development of models for a better representation of real processes is the core of the further development of the simulation software. Model development is done on the chemical engineering side but also in control engineering and for the improvement of mathematical simulation techniques. Process simulation is therefore one of the few fields where scientists from chemistry, physics, computer science, mathematics, and several engineering fields work together [25]. 1.14 Develop a new model A lot of efforts are made to develop new and improved models for the calculation of properties. It includes the description as following [25] Thermo physical properties like vapor pressures, viscosities, caloric data, etc. of pure components and mixtures. Properties of different apparatuses like reactors, distillation columns, pumps, etc. Chemical reactions and kinetics. Environmental and safety-related data. 1.15 Types of Models Two main different types of models can be distinguished: Rather simple equations and correlations where parameters are fitted to experimental data. Predictive methods where properties are estimated [25]. The equations and correlations are normally preferred because they describe the property (almost) exactly. To obtain reliable parameters it is necessary to have experimental data which are usually obtained from factual data banks or, if no data are publicly available, from measurements. Using predictive methods is much cheaper than experimental work and also than data from data banks. Despite this big advantage predicted properties are normally only used in early steps of the process development to find first approximate solutions and to exclude wrong pathways because these estimation methods normally introduce higher errors than correlations obtained from real data. Process simulation also encouraged the further development of mathematical models in the fields of numeric and the solving of complex problems [26]. 1.16 History of Simulation The history of process simulation is strongly related to the development of the computer science and of computer hardware and programming languages. Early working simple implementations of partial aspects of chemical processes were introduced in the 1970s when suitable hardware and software (here mainly the programming languages FORTRAN and C) became available. The modelling of chemical properties began much earlier, notably the cubic equation of states and the Antoine equation were precursory developments of the 19th century [26]. 1.17 Steady State and Dynamic Process Simulation Initially process simulation was used to simulate steady state processes. Steady-state models perform a mass and energy balance of a stationary process (a process in an equilibrium state) it does not depend on time [26]. Dynamic simulation is an extension of steady-state process simulation whereby time-dependence is built into the models via derivative terms i.e. accumulation of mass and energy. The advent of dynamic simulation means that the time-dependent description, prediction and control of real processes in real time has become possible. This includes the description of starting up and shutting down a plant, changes of conditions during a reaction, holdups, thermal changes and more [26]. Dynamic simulations require increased calculation time and are mathematically more complex than a steady state simulation. It can be seen as a multiply repeated steady state simulation (based on a fixed time step) with constantly changing parameters [26]. Dynamic simulation can be used in both an online and offline fashion. The online case being model predictive control, where the real-time simulation results are used to predict the changes that would occur for a control input change, and the control parameters are optimized based on the results. Offline process simulation can be used in the design, troubleshooting and optimization of process plant as well as the conduction of case studies to assess the impacts of process modifications [26]. 1.18 List of Chemical Process Simulators Aspen Plus Aspen HYSYS CHEMCAD COCO Simulator ASSETT PRO/II ProSimPlus SolidSim Aspen Plus Aspen plus is one of the industry’s leading process simulation software. Aspen Plus is a comprehensive chemical process modeling system, used by the world’s leading chemical and specialty chemical organizations, and related industries to design and improve their process plants. Aspen Plus boasts the world’s most extensive property database and handles solid, fluid and gas phase processes -- making it the best choice for chemicals, polymers, specialty chemicals, pharmaceuticals and biotech, biofuels, power, carbon capture, minerals, metals and mining [27]. Aspen Hysys Aspen Hysys is a comprehensive process modeling system used by oil and gas producers, refineries and engineering companies to optimize process design and operation. Aspen HYSYS is an easy-to-use process modeling environment that enables optimization of conceptual design and operations. Aspen HYSYS has a broad array of features and functionalities that address the process engineering challenges of the energy industry. The best modeling environment for the energy industry is now easier to use than ever before. Experience activated economics, energy analysis heat exchanger design and rating, and dynamics to optimize in minutes and realize more value [27]. ChemCad This sophisticated software package can be used in almost every aspect of process engineering from design stage to cost and profitability analysis. It has a built-in model library for distillation columns, separators, heat exchangers, reactors, etc. Custom models can extend its model library. These user models are created with FORTRAN subroutines or Excel worksheets and added to its model library. Using Visual Basic to add input forms for the user models makes them indistinguishable from the built-in ones. It has a built-in property databank for thermodynamic and physical parameters. During the calculation of the flow sheet any missing parameter can be estimated automatically by various group contribution methods [27]. COCO Simulator The COCO Simulator is a free-of-charge, non-commercial, graphical, modular and CAPE-OPEN compliant, steady-state, sequential simulation process modeling environment. It was originally intended as a test environment for CAPE-OPEN modeling tools but now provides free chemical process simulation for students. It is an open flow sheet modeling environment allowing anyone to add new unit operations or thermodynamics packages. The COCO Simulator uses a graphical representation, the Process Flow Diagram (PFD), for defining the process to be simulated. Clicking on a unit operation with the mouse allows the user to edit the unit operation parameters it defines via the CAPE-OPEN standard or to open the unit operation's own user interface, when available. This interoperability of process modeling software was enabled by the advent of the CAPE-OPEN standard. COCO thermodynamic library "TEA" and its bank are based on ChemSep LITE, a free equilibrium column simulator for distillation columns and liquid-liquid extractors. COCO's thermodynamic library exports more than 100 property calculation methods with their analytical or numerical derivatives. COCO includes a LITE version of COSMO term, an activity coefficient model based on Ab initio quantum chemistry methods. The simulator entails a set of unit-operations such as stream splitters/mixers, heat-exchangers, compressors, pumps and reactors. COCO features are action numerics package to power its simple conversion, equilibrium, CSTR, Gibbs minimization and plug flow reactor models [27]. PRO/II PRO/II from the Schneider Electric SimSci brand is a steady-state process simulator (process simulation) for process design and operational analysis for process engineers in the chemical, petroleum, natural gas, solids processing, and polymer industries. It includes a chemical component library, thermodynamic property prediction methods, and unit operations such as distillation columns, heat exchangers, compressors, and reactors as found in the chemical processing industries. It can perform state mass and energy balance calculations for modeling continuous processes [27]. As with any process simulation product, Key Benefits include: [27]. Rigorously evaluate process improvements before committing to costly capital projects. Improve plant yields through the optimization of existing plant processes. Cost effectively assess, document and comply with environmental requirements. Accelerate process troubleshooting. Detect and remedy process bottlenecks. ProSim ProSim is a leading European engineering Software Company delivering chemical process simulation software and consulting services to the energy, oil, gas, chemical, petroleum, pharmaceutical, food & beverage and other processing industries worldwide.  ProSim solutions are used to improve process design, increase plant efficiency and reduce their impact on environment. Thanks to long term partnerships with major research centers and to substantial investment in R&D, ProSim continuously develops innovative software and has become a recognized player on the international market. ProSim is the premium alternative in Process Simulation and Optimization as following [27]. Ease of use Ability to quickly get accurate output with tentative input , this saves time and cost Rough approximations still yield results, and as more information becomes available the process can be further refined Heat and material balances for well-defined processes are as precise as any other simulator Short term engineering tasks rely on quick accurate results from a rigorous self-documenting calculation within CHEMCAD CHEMCAD can be used by anyone in the organization because it is simple and intuitive CHEMCAD offers valuable interfaces to Excel CHEMCAD is more flexible than Aspen for user unit operation for Spec Sheets for reports for Data Reconciliation (validating of plant data for optimization) for online simulation (automatic control of a plant) for Management planning CHEMCAD is clearly less expensive than Aspen and our institute has a license to use it. 1.19 Advantages of Simulation Advantages of simulation as following [28]: Improved process efficiency Increased operational system availability Transportation avoidance Reduced eliminated expendable costs Effectiveness to the process Improved proficiency performance Saves time and money Improves the quality of analysis Try out many alternatives Risk reduction in safety, environment and equipment. Chapter 1: Introduction 26