feasibilty for the project.docx

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SIR WILLIAM CROOKS addressed the problem and concluded with the words: “ It is the

chemist who must come to the rescue of the threatened communities. It is through the

laboratory that starvation may ultimately be turned into plenty. Before we are in the grip of

actual dearth the chemist will step in and postpone the days of famine to so distant a period

that we, our sons and grandsons may live without undue solicitude for the future.”

Ammonia is one of the largest 5 commodities of chemical industry. Where there is

nitrogen required for chemical production it comes from Ammonia. 15% of the

chemical industry commodity is fulfilled through Ammonia.

Synthetic ammonia produced from reaction between nitrogen and hydrogen is the base

from which virtually all nitrogen-containing products are derived.

Fixed nitrogen from the air is the major ingredient of fertilizers which makes intensive food

production possible. During the development of inexpensive nitrogen fixation processes,

many principles of chemical and high-pressure processes were clarified and the field of

chemical engineering emerged.

Present Scenario: (Need of the Day)

Non supply of gas to Fertilizer Sector is hurting farmers as well as agriculture sector of

economy besides causing maximum urea price hike. Higher input costs and lower produce

prices have started crippling farming community. Fertilizer expenses saw the maximum

increase among all inputs during last year. Pakistani industries which produce ammonia

1. Engro Fertilizers

2. Fauji Fertilizers

3. Agri Tech

4. Dawood Hercules

5. Reliance Group

6. National Fertilizer Marketing Ltd

Ammonia Synthesis: A Brief over view can be as follow:

1. Different feed stocks available and cost comparison.

2. Technology wise discussion

3. Selection of feed stock

4. Cost estimation

5. Selection of the Process on the behalf of the above stated discussion.



Progress in Ammonia synthesis can be divided into 3 phases

1. Haber Era

2.

Development in Catalyst.3. Future Prospectus

Haber’s Contributions to Ammonia Synthesis Process

Haber recognized that much higher pressures had to be employed and he constructed a small

laboratory apparatus for the continuous production of ammonia. Haber’s recycle idea

changed the previously static conception of process engineering in favor of a more dynamic

approach.

Schematic of re-cycle apparatus used by Haber for ammonia synthesis

The amount of ammonia formed in a single gas pass is much too small to be of interest for

the economic production of ammonia. Haber, therefore, recycled his gas over the catalyst

after separating the ammonia formed by condensation. The gas lost by conversion was

compensated with a fresh gas input and the mixture was recycled under pressure. This

process became the basis for the technical manufacture of ammonia. Since then, the same

principle has found widespread application for numerous high-pressure reactions in the

organic chemistry sector. Haber’s recycle idea changed the previously static conception of

process engineering in favor of a more dynamic approach. For the first time, reaction

kinetics as well as the thermodynamics of the system was being considered. In addition tochemical equilibrium, Haber recognized that reaction rate was a determining factor in this



problem. Instead of simple reaction yield, he concentrated on space-time yield, that is, the

amount of ammonia obtained per unit volume of the catalyst per unit time (Figure 3).In this

manner it became apparent that the real problem was to find a suitable catalyst so that the

maximum amount of product is obtained with minimum volume of the catalyst in the shortest

time possible, that is, space time yield needs to be maximized. Early in 1909, Haber discovered in finely distributed osmium, a catalyst which yielded 8% ammonia at 175 bar and

about 600°C. He also established that uranium could be used as a catalyst. Haber constructed

a new laboratory plant which could be operated according to his recycle concept (Figure4).

With this equipment, he demonstrated the production of 80 g of ammonia/ hr in July 1909.

The catalysts which Haber initially employed were too expensive and unstable to be used in

commercial processes. Systematic investigations covering virtually the en-tire periodic table

by Haber, Metcash and coworkers at BASF for next two years resulted in solution to the

catalyst problem.

In early units the reactor was heated externally, by gas burners, although this had thedisadvantage of further weakening the shell.

• A special air burner at the top of the catalyst bed could increase the gas temperature and

was used until 1922, despite the poisoning effect of water on the catalyst.

• Larger reactors only used a gas heater at start-up with reverse gas flow to avoid catalyst

poisoning.

• From 1920 better steel alloys that resisted embrittlement

became available.

By 1925, new reactors had been developed by usingimproved chromium vanadium steel alloys and internal heat

exchangers. The outer shell was protected from overheating

by passing the cold synthesis gas down the annular space

between the shell and the catalyst basket as it entered the

vessel. A typical plant was operated with the catalyst

temperature in the range 500 0 – 6500 C and at a higher

pressure, up to 300 – 350 atm, which allowed higher

conversion and easier ammonia removal by water scrubbing.

While these conditions should give a theoretical conversion

in the range 8 – 11%, the actual conversion was only 7 – 9%.

A reactor, producing 20 tons .day of ammonia weighedabout 70 tones, was 12 m long, and held a basket of 80 cm

internal diameter. It took about 3 days to change a

deactivated catalyst and restart operation. In those days, in

order to increase production, typical ammonia plants

operated with several small reactors rather than a single

large one.

The production of ammonia during the early 1900s stimulated the increasing use of industrial

catalysts. Development of the synthesis catalyst set a pattern for all other catalysts

subsequently used in chemical and refining processes. Theoretical and experimental effort

had shown that the process was feasible. This was followed by the development of practicalequipment and full scale operation. A relatively cheap and reliable catalyst was thoroughly



tested and Produced economically in what were then large volumes. Finally, both the process

and catalyst were gradually improved as the scale of operation expanded.

The pioneering work of Haber, Bosch, and Metcash led to a process which has survived in

more or less the same form as it is used today. Their achievement led to the introduction of

chemical engineering, high pressure technology and consolidated the ideas of unit processes. New materials were developed for use with hydrogen at high pressures.

Process Development

Today the term “ammonia synthesis” is increasingly used when referring to the total

ammonia production process. Synthesis conditions are no longer viewed in isolation. Of

course, they are an important consideration in the total process but can be determined

properly only in relation to the total plant integration.

The complete process of industrial ammonia production may be subdivided into the following

sections:

1. Raw synthesis Feed gas purification

a. Desulfurization (by hydro-treating and absorption)

b. Reforming (primary and secondary) as well as Pre-reforming.

c. Carbon monoxide (CO) shifts to carbon dioxide.

2. Synthesis Feed gas purification

a. CO2 removal by Absorption. Conversion of CO and trace amounts of CO2 (Total

Oxides) by Methanation.

3. Liquid Ammonia Synthesis ( Production)

a. Compression of synthesis feed gas.

b. Synthesis (conversion) of syn. Gaas to ammonia.

c. Separation of liquid ammonia from the syn. Gas loop (chilling).

4. Removal of Light ends (Low Pressure flash and Re-Flashing.

Table 1 Historical Development in Ammonia synthesis

Designation Pressure Temp.0C

Catalyst Recirculation Conversion

%

Haber-Bosch 200-350 550 Doubly

Promoted

Yes 8

ModifiedHaber-Bosch

200-300 500-550 -Do- Yes 20-22

Claude 900-1000 500-650 Promoted

iron

No 40-85

Casale 600 500 Promoted

iron

Yes 15-18

Fauser 200 500 Promoted

iron

Yes 12-23



Table 2 Feed stock distribution of world a historical review

Relative Ammonia plant investment and relative energy requirement for 1800 t/d NH3

Table 3

Table 2 provides an overview of the raw material sources (apart from water and air)

For world ammonia capacity.

Table 3 indicates that new ammonia plants are based almost exclusively on natural gas

and naphtha. This trend is also expected to continue in the near future.

Table 4 Different technologies modernization of Ammonia synthesis

Specific Energy Requirement Comparison

Table 5 Hydrogen generation Raw Material



Figure 1 Ammonia capacity by feedstock

Figure 2 Different roots to Produce Syn gas



Figure 3 Options for generating and purifying ammonia synthesis gas



Figure 4 Block diagram and gas temperature profile for a steam reforming process

Table 6 Main Energy Sources and sinks in the steam reforming ammonia process

There are three configurations

1. Minimum Energy Consumption

2. Realistic concept of low energy3. Low investment cost



Table 7 Energy Consumption in Different Process configuration

Figure 5 Comparison of LAC process with a conventional process

Adiabatic Pre-Reforming

This method in case of vaporized naphtha feed is done to decompose the higher hydrocarbon

in to lower once, like CH4 and the other components like H2, CO & CO2. The vaporized

naphtha is mixed with steam and preheated to about 490c. The gas is passed through the pre-

reformer containing Ni catalyst. The typical composition of the pre-reforming catalyst is Ni-25%, Al2O3-11%, MgO-balance.

In the pre-reformer the endothermic reforming reactions are followed by the exothermic

Methanation and the shift reaction. The over all process is normally exothermic. The gas

from adiabatic pre-reformer is sent to primary & secondary reformer for further reforming.

The adiabatic pre-reformer reduces the head loss on the primary reformer, thus the life of

reformer tubes longer. Pre-reformer also acts as an efficient sulfur guard for the primary

reformer catalyst.



Partial Oxidation of Heavier Hydrocarbons

Hydrocarbons heavier than naphtha can be used as feed stocks for ammonia production by

partial oxidation process. Natural gas and naphtha also can be used, but since the plant cost

for partial oxidation process is considerably higher than that for steam reforming, the lighter

feedstock is seldom used. And there is more fluctuation due to carbon soot formation. In spiteof it, it has advantage of wider choice of feedstock with greater tolerance for impurities.

Crude petroleum can be used as feed stock; most common feedstock can be heavy residual oil

from petroleum refining processes, which has had more light ends removed.

It has high sulfur contents. It involves expensive equipments for pollution abatement

regarding environmental impacts.

Figure 6 FLow diagram of partial oxidation scheme



New Catalyst Developments

At the stage of development of the ammonia synthesis reaction as described in the previous

sections, the main problem was the low level of conversion of synthesis gas to ammonia .

This could be increased by operation at yet higher pressure, but this would not be cost

effective. The other option would be to operate at lower temperature, under which conditions,the equilibrium concentration of ammonia would be appreciably higher. Unfortunately, the

catalysts available at the time were not sufficiently active to operate at the lower temperature

required to make a meaningful difference to the concentration of ammonia in the product gas,

and hence a significant difference to the economics of the process. Any real improvement to

the process was therefore dependent upon the development of a new catalyst with

significantly improved activity. The clear target would be a catalyst with sufficient activity to

give a satisfactory level of conversion at the same pressure as that within the reformer.

The surface area of the ammonia synthesis catalyst is only about 1 – 2 m 2 g -1 . It was known

from experience with other catalysts that precipitation from aqueous solution always led to a product with a much higher surface area than one prepared by fusion, and therefore

potentially at least, more active sites per unit weight of catalyst. This process route was

studied in ICI, initially by Topsham. Subsequent developments led to the preparation and

testing of a precipitated catalyst containing cobalt which showed levels of activity

approximately 3 fold higher that of the best conventional catalyst available at the time.

Ammonia could be synthesized at temperatu res below 350ºC , but the catalyst was not

commercialized for several reasons. The major reason was that the pelleted oxide was

signi f icantly weakened dur ing the reduction procedure, and became too weak to withstand

the rigours of an axial f low converter. I t also suf fered fr om shr inkage dur ing reduction,

leading to settl ing of the bed, and the li kely development of hot-spot s.

The announcement in 1979 by BP of a ruthenium catalyst was the first real advance in

improving the process. The catalyst was more active and operated at a lower temperature to

produce a higher equilibrium ammonia concentration. A relatively high operating pressure

was still needed, however, when using a bed charged with Ru catalyst in conjunction with

other beds containing magnetite catalysts. The catalyst was reversibly poisoned by some of

the impurities pre-sent in typical synthesis gas.

The new ruthenium catalyst converter was in series with the old converter. Although in 1992

there was no additional synthesis gas to increase production capacity, the ruthenium catalyst

operated well in a radial flow reactor and reduced both the steam and electricity used by 30-

40% and 5-10% respectively. The new catalyst was said to be twenty times as active as the

iron catalyst, and the effluent gas contained about 20% ammonia.

Other large ammonia plants are now using single beds of the ruthenium catalyst in

conjunction with the magnetite catalyst. They confirm the higher activity of ruthenium, with

the benefits of a lower operating pressure and temperature, while maintaining a high

concentration of ammonia in the exit gas. For future process designs, the need for less gas

compression and less high-pressure equipment will lead to lower operating and capital costs.



Two plants in Trinidad, using one bed of iron catalyst and three beds of ruthenium catalyst,

have operated for several years. It is reported that the capacity of typical 1100 tones per day

plant designs could be increased to 1850 tones per day, provided there is suf fi cient reformer

capacity.

Table 8 Introduction of Ammonia Plant catalysts and Operating life

Converter Design

The majority of early ammonia plants used adiabatic beds of catalyst or tube-cooled

converters that acted like a heat exchanger with the cold synthesis gas passing through thetubes to cool the catalyst. Tube-cooled reactors, such as those introduced by the Tennessee

Valley Authority (TVA), did not operate isothermally and the exothermic reaction led to both

axial and radial temperature profiles developing. The temperature difference depended on the

number of tubes passing through the catalyst bed. The converter design took this into ac-

count by maximizing the number of tubes although the temperature profile could only be

controlled by changing the inlet gas temperature. There were problems in loading catalyst

into the space between tubes to achieve the right packing density as well as in discharging

catalyst when it was deactivated. Large tube-cooled converters were also expensive.

Modern converters are designed with several catalyst beds in which the hot gas can be cooled

at each bed exit either by heat exchange or by the addition of cold synthesis gas, often

referred to as quench cooling Quench cooling has usually been preferred in plants using

multi-bed converters despite the disadvantage of using a larger catalyst volume and having to

by-pass some of the catalyst with a significant volume of the synthesis gas.

Problems were experienced in wide, multi-bed converters, with gas flowing axially through

the beds, because big catalyst particles were required to limit the pressure drop through the

catalyst. Since activity is inversely proportional to particle size, increased volumes of catalyst

were needed and the large reactors increased the capital cost of a plant. By designingconverters in such a way that gas flowed radially through the catalyst bed, it was possible to



decrease the overall pressure drop and to use smaller catalyst particles that did not suffer

from the limitations of pore diffusion to the same extent, and thus showed greater activity per

unit volume. Gas distribution problems in the top bed resulting from a low-pressure drop

were overcome by the use of an improved converter design. In one case, an axial-radial flow

system was used. In another, transverse gas through catalyst bed horizontal convertor wasused.

The ICI cobalt catalyst, which is reported to contain 10-20% cobalt oxide, was developed for

use at 80 bar synthesis pressure and maximum temperatures as low as 460°C. These

conditions were significantly different from the usual single-stream ammonia plants which

operated at 150 bars or higher and temperatures up to 500°C. From experimental work with

precipitated cobalt-iron catalysts it appeared that the cobalt reacted with alumina giving

cobalt spinals, which helped to form smaller iron and cobalt crystallites during reduction and

to increase the surface area to make the catalyst more stable and less sensitive to oxide

forming poi-sons. In the presence of potash, cobalt was able to decrease the reductiontemperature. Development work was successful and, following a typical fusion production

procedure, the new catalyst could be reduced and operated at lower temperature under normal

conditions in conventional plants. Reduction began at 380°C in the new AMV and LCA

processes introduced by ICI in 1985 and 1988 respectively. The AMV plants have operated at

more than 100% capacity of a pressure of only 60 bar. The life of the new catalyst has been

very satisfactory, and could be operated of pressures much closer to those of the reformers,

albeit with large converters.

Table 9 Different timely approaches for Convertor design



Applications of Ammonia

At the start of the millennium about 85% of ammonia production was consumed for

fertilizers. Ammonia is either converted into solid fertilizers (urea; ammonium nitrate,

phosphate, sulfate) or directly applied to soil.

Industrial use of ammonia is around 15%. Actually every nitrogen atom in industrially

produced chemical compounds comes directly or indirectly from ammonia. An important use

of the ammonia nitrogen, partly after conversion to nitric acid, is the production of plastics

and fibers such as polyamides, urea-formaldehyde-phenol resins, melamine-based resins,

polyurethanes, and poly-accryl-o-nitrile.



Some examples of industrially important uses are the following reactions:

With alkyl halides or alcohols amines or imines can be manufactured. For example, methanol

forms mono-through trimethylamine, dichloromethane yields ethylene imine in the presence

of calcium oxide. Amines can also be produced by reacting ammonia with alkyl halides in

multistage process.

Environmental sector ammonia is used in various processes for removing SO2 from flue

gases of fossil-fuel power plants. The resulting ammonium sulfate is sold as fertilizer. In the

selective catalytic reduction process (SCR) the NOx in the flue gas is reduced in a catalytic

reaction of nitrogen oxide with a stoichiometric amount of Ammonia.

Figure 7



Figure 8 A quick comparison of different application of ammonia

Table 10 Composition and Properties of Representative Sample of Naptha



Figure 9 Component of ammonia production

A Quick Comparison

Feed Stock

Technology Rel.Capital Investment

Feedstock Ton/ton

RelativeCost/ton

Relative EnergyConsumption

Energy(Gcal)

Lower Heating value

Natural

gas

Steam

Reforming

1 0.624 1 1 7.0 11000

Naphtha Steam

Reforming

1.15 0.720 2.5 1.1 7.6 10556

Coal Gasification 2.5 1.4 1.5 2.0 13 6000

The most suitable feedstock for the next 2 decades is surely natural gas. Naphtha due to its

high price can not be taken alone as feed stock but for some compensation and to avoid

fluctuation in the plant operation. A mixed feed of Naphtha and natural gas can be considered

as feed stock. Coal is also indigenous raw material abundantly available, but the plant taking

coal as feed stock is not self stand on the behalf of its energy requirements. About 650

Kwatt-hour extra energy is required for plant operations.

A review of ammonia production technology up to 1974 is contained in, and gives a

description of the state of the art up to 1980; the United States patent literature in the field

from 1972 to 1980 is covered in More modern and comprehensive reviews of ammonia

production technology can be found in [402]- [404]. The journal Nitrogen, published by

British Sulphur, presents an update of the state of the art from time to time. A valuable

information source is also the annual AIChE Ammonia safety symposium.

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