UNIVERSITI MALAYSIA PAHANG

FACULTY OF INDUSTRIAL SCIENCES AND TECHNOLOGY

BSK 3163

INORGANIC CHEMISTRY PROCESS

PROJECT

PROCESS IMPROVEMENT THROUGH PROCESS INTEGRATION AND INTENSIFICATION

IN SULPHUR INDUSTRIES

(CLAUS PROCESS)

NAME ID NO

NOOR AZIZAH BT MD JENAL SA10101

NURUL NAJWA BTE MUSTAFA SA10100

LECTURER NAME : PROF DR MOHD RIDZUAN BIN NORDIN

DATE OF SUBMISSON : 3 DISEMBER 2012

1.0 Introduction

Recovery of elemental sulphur from acid gas was first performed via the Claus process

over 100 years ago. Many researches are done by do some Claus modifications which can

alleviate operational difficulties and improve overall sulphur recovery. The Claus process has

been the standard of the sulphur recovery industry, but limitations and problems relating to

composition may restrict its effectiveness. Numerous modifications hand improvement has been

applied to the basic process in an effort to develop the optimum system for a certain set of

conditions.

2.0 Definition of Process Improvement in Chemical Industries

Process design trends or process improvement in chemical industry are related to the

development of more efficient technologies. Two type’s most important approaches are process

integration and process intensification.

Process integration looks for the integration of all operations involved in the production

of one specific product. This can be achieved through the development of integrated processes

that combine different steps into one single unit. When several operations can be carried out in

a same single unit, the possibilities for improving the performance of the global process are

higher, especially if energy costs are considered.

Process intensification we can define as an engineering expression that refers to making

changes that render a manufacturing or processing design substantially improved in terms of

energy efficiency, cost-effectiveness or enhancement of other qualities.

3.0 Process improvement in Claus process

3.1.1 Process Integration

Sub dew point Claus process

The conventional Claus process described above is limited in its conversion due

to the reaction equilibrium being reached. Like all exothermic reactions, greater

conversion can be achieved at lower temperatures, however as mentioned the Claus

reactor must be operated above the sulfur dew point (120–150°C) to avoid liquid sulfur

physically deactivating the catalyst. To overcome this problem, the sub dew point Claus

process operates with reactors in parallel. When one reactor has become saturated with

adsorbed sulfur, the process flow is diverted to the standby reactor. The reactor is then

regenerated by sending process gas that has been heated to 300–350°C to vaporize

the sulfur. This stream is sent to a condenser to recover the sulfur.

3.1.2 Process Intensification

In this process, the use of hydrogen is important to achieved higher flexibility. Not only

that, the refiners will be minimizing for new development to change economy environment and

to maximize output from existing equipment. In process improvement through process

intensification, hydrogen used is quite limit but now, this change over time because :

a) To reduce the excess capacities for better economy. This new environmental law

utilizes the heavy feed oils. For Claus process, it receives sulphur more than

ammonia from hydrotreaters which currently defined in process intensification.

b) The higher volatility of crude oils and product prices is the reason for greater

flexibility on refiners.

c) The oxygen gas residue allows full conversion of crude oil to produce valuable

products. This can make it more flexible and efficient.

A tail gas clean-up process

In the conventional Claus process is about 94% to 98% efficient in removing H2S. Many

improvements have been developed to allow the process to obtain 99+% conversions, as

emission limitshave tightened. A tail gas clean-up process is often used. An example is the

amine-based tailgascean-up process, which reduces all of the sulfur compounds in the tailgas

leaving the front-end Claus sulfur plant back to H2S, then uses selective amine absorption to

remove the H2S while allowing most of the carbon dioxide to slip by. The H2S and carbon

dioxide removed by the amine are stripped from the amine and recycled back to the Claus plant,

allowing an overall sulfur recovery in excess of 99.5%.

Superclaus catalyst

The Superclaus catalyst is designed to give complete and highly selective conversion

of H2S to elemental sulfur, low formation of SO2, and low sensitivity to water concentrations in

the process gas so it has no Claus reaction reactivity. The catalyst consists of active metal

oxides on a carrier. Its properties include the following: H2S conversion to sulfur higher than

85%, not sensitive to excess air, not sensitive to high water concentrations, no Claus reaction,

no CO/H2 oxidation, no formation of COS/CS2, and chemically and thermally stable with good

mechanical strength and long effective life. Two options for the Superclaus process are the

Superclaus 99 and the Superclaus 99.5 processes. Superclaus 99 consists of a thermal stage

followed by three or four catalytic reactor stages, much like the Claus process. The first two or

three catalytic stages are loaded with the standard Claus catalyst while the final stage is loaded

with the new selective oxidation catalyst. In the Superclaus 99.5 process, a hydrogenation stage

(using a cobalt/molybdenum catalyst) between the last Claus reactor and the selective oxidation

reactor is added. Sulfur recovery in the Superclaus 99 process with 2 Claus stages is in the

range of 98.9% - 99.4% and in the range of 99.3% - 99.6% with 3 Claus stages. Sulfur recovery

in the Superclaus 99.5 process is in the range of 99.2% - 99.6% with 2 Claus stages and 99.4%

- 99.7% with 3 Claus stages.

Oxygen Enrichment Of Sulfur Recovery Units (Sru)

The underpinning theoretical concept that makes oxygen enrichment such an effective

means of briefly explained when in the Claus process, about one-third of the hydrogen sulfide in

the acid gas stream is combusted to sulfur dioxide which further reacts with the remaining

hydrogen sulfide to form elemental sulfur and water in the vapor phase. The combustion

reaction and approximately 60-70% of the conversion of hydrogen sulfide to sulfur, take place in

the thermal reactor at temperatures between 1100°C and 1400°C for typical refinery acid gas

streams. The remaining equilibrium conversion of hydrogen sulfide to sulfur takes place in a

series of catalytic reactors at much lower temperatures. Representative reactions are

summarized below

H2S + 3/2 O2 SO2 + H2O (Combustion reaction)

2H2S + SO2 3S + 2H2O (Claus reaction)

__________________________________________

3H2S + 3/2 O2 3S + 3H2O (Overall reaction)

Let’s, stoichiometrically, 100 kmol/h of hydrogen sulfide requires 50 kmol/h of oxygen. If

all of the oxygen is provided by the air, 189 kmol/h of nitrogen comes along with the 50 kmol/h

of oxygen. This nitrogen (over 50% by volume in the feed) contributes to a large amount of the

pressure drop through the SRU due when an SRU is bottlenecked by hydraulic or residence

time limitations, oxygen enrichment of the combustion air reduces the nitrogen flow through the

SRU, thereby allowing an increase in the acid gas and sour water stripper gas stream.. It also

increases the temperature in the first Claus step, a furnace. This allows for a more effective

destruction of NH3 within this thermal section, thus contributing to the long-term stabilization of

the Claus operation.

Partial oxidation

Partial oxidation with function is to convert liquid or solid hydrocarbons to hydrogen,

carbon monoxide, carbon dioxide and water by gasification. After that, the gas will be used as

synthesis gas or fuel gas and also as crude gas for hydrogen recovery.

In this process development, partial oxidation can have some possibilities for refinery

operators. Below are some possibilities that have been found in the sulphur industry. There are :

a) Heavy heating oil’s and residues in particular can be used as feedstock to partial

oxidation plants in refineries which can be operated practically with no limit to the

pollutant content. This possibilities can help feedstock can be used economically.

b) The other possibility is the gas form partial oxidation can be used for fuel in an

integrated gasification combined cycle power plant. This type of power plant

particularly high efficiency and its emissions are low from pollutant.

c) Gasification gas from partial oxidation can also be used as a synthesis gas because

after appropriate pre-treatment, usually synthesis of gas to liquid, production of

synthetic diesel or gasoline, for methanol or for ammonia production. The partial

oxidation used to produce chemicals also broadens the economic base of the

refinery.

d) Besides that, partial oxidation can handle differing feedstock compositions, within

wide limits. It was possible to use crude oil of different qualities in the refinery and to

feed residues that cannot be utilized economically in the usual refining procedure.

Advantage use of oxygen in partial oxidation

Thus, the refinery operator can bring several advantages in sulphur industries. The

advantage of this are state below :

a) Cleaner and more advantageous reuse of residues.

b) Broadening of the economic base of the refinery.

c) Wider range of products and thus greater economic flexibility of the refinery.

d) A wider range of crude oil compositions to be processed.

4.0 The Cost and Benefit of Improvement Process

A tail gas clean-up process

This technologies improvement has been developed to increase total sulphur removal

above 96% for basis Claus Unit. The larger number available choice require refiners to evaluate

increased sulfur discovery based on their specific needs versus the increase in capital and

operating cost of increased recovery.

Superclaus catalyst

This catalyst if function to give complete and highly selective conversion of H2S to

elemental sulfur, low formation of SO2 and low sensitivity to water concentrations in the process

gas. Other than that, higher activities have been achieved with catalysts that provide higher

surface areas and macro porosity

Oxygen Enrichment of Sulfur Recovery Units (Sru)

The most common driver for implementing SRU oxygen enrichment is to increase

processing capacity. The reduction of diluent nitrogen results in higher partial pressure of

hydrogen sulfide (H2S) in the process stream, which leads to higher conversions in the SRU

catalytic reactors. Also, the relative SRU tail gas flow rate is progressively reduced as oxygen

enrichment is increased. The reduction in nitrogen entering the Tail Gas Cleanup Unit (TGCU)

results in higher hydrogen sulfide partial pressures in the amine absorber. This results in better

absorption and lower sulfur emissions than the air-based SRU operation. For the capital cost

saving, depending on the enrichment technology, the cost of implementing SRU oxygen

enrichment is only 5-20% of the cost for building a new SRU. Oxygen enrichment can also be

economical for grassroots plants due to smaller equipment for the same capacity.

Then for time saving, SRU oxygen enrichment can be implemented quickly. No “down

time” is required for low-level enrichment (up to 28% oxygen in air) as an oxygen diffuser can be

hot tapped into the air main. For higher levels of oxygen enrichment tie-ins and modifications

can be achieved within the timing of a normal turnaround. Oxygen-enriched operation has

proven to be both reliable and safe regardless of the chosen technology

Partial oxidation

A long time ago, the principle users of the heavy oils and residues were power plants

and ships but it vanishing because the users must also convert to lower sulphur fuels. This cost

of burning is high due to sulphur fuels in power plants are steadily increasing because

requirements of purity waste gases are increasing instead of the cost purification. Due to

increasing of higher costs of low sulphur fuels, the power plant operators often find that can

reduced cost of waste-gas clean up makes them more economical than cheaper but higher

sulphur fuel. Both developments means that the refinery operator either cannot sell high-sulphur

heating oil’s or residues at all or it can sell them only at low price is depends on both improve

the refinery hydrogen balance and economically get rid of high-sulphur oil’s and residues.

Basically, a refinery with a crude oil capacity of 10 million can supply an IGCC power

plant with a power of about 350Mw. This can give the refinery another leg to stand and broaden

the economic base. The refinery can also react more flexibly to market requirements.

Not all the refinery has its partial oxidation unit because in spite of these advantages, the

high capital investment for such a unit and that it must result in greater economic utility before

involve with existing structure of a refinery. This occur especially for GTL, the fast rising crude

oil price made production of these synthetic fuels increasingly more attractive and of course, this

additional ultraclean fuel fits perfectly into the palette of product refinery.

Conclusion

As a conclusion, the sulphur industry refinery consist three bed basic Claus process that

can be used for rich acid gas feeds but currently emission regulations required 99% and above

sulphur recovery to modification in the traditional Claus process or the addition of a secondary

tail gas cleanup process. Lean acid gas feeds require a modification to the operation of the

burner to produce temperature high enough to promote stable combustion.

Other methods such as a catalytic "burner" may be used in place of the traditional burner

in some instances. To achieve the optimum Claus process design for any feed composition, all

suitable processes should be fully explored with a process simulator before making design

decisions.

References

1. Reinardt, H. J., and Heisel, M. (1999). "Increasing the capacity of Claus plants with oxygen,"

Linde Reports on Science and Technology, No. 61, p. 2 ff.

2. Paskall, H.G., and Sames, J.A. (2009). "Sulfur recovery by the modified Claus process," The

Sulphur Experts, 12th Edition, Calgary.

3. Perez, Haro., Juan et al.(1992). "O2 enrichment increases FCC operating flexibility," OGJ, p.

40

4. Sadeghbeigi, R.(1995) "Fluid Catalytic Cracking Handbook," Houston: Gulf Publishing.