Design of sulphur recovery - Part 1( project done in CPCL)

ABSTRACT

 

             This project is about sulphur recovery process being carried out from the acid gas which is the exhaust of refinery process. Sulphur removal and therefore its recovery is need of the hour from Pollution and Environmental point of view. Earlier sulphur gas produced as a result of several Industrial Operation was directly flared into atmosphere which led to serious environmental problems causing damage even to human life.

            In this  project  the two technologies of sulphur recovery namely CLAUS PROCESS  and MAXIMUM  CLAUS  REOVERY CONCEPT (MCRC) are being combined  for the flow rate of 3740kg/hr.

            Earlier CLAUS process was used with a efficiency level of  94% but  now Maximum Claus  recovery concept  is utilised in which the efficiency level is increased to 99.5% of Sulphur  being recovered.

            Process flow sheet is being attached as Annexure. On this flow sheet  Mass and Energy balance are calculated, and  equipment are designed as per requirement. Process control, Environment issues and safety measures are described in the report. Cash flow analysis is also computed.

Need for the project :

1.     Sulphur present in the refinery off gas principally as H₂S .

2.     Sulphur found in most of petroleum crudes in variable amounts generally compounds are present in more quantities in higher molecular weight stockes .

3.     Sulphur occupies prominent position in refining due to its problems of corrosion and odour .

4.     Pollution problems and cost of waste treatment is punitive for all refineries with high Sulphur stocks .

HISTORY OF THE PROCESS :

1.     Sulphur recovery is a combination of classical Claus process & Maximum Claus recovery concept (MCRC) .

2.     Claus process as used today is a modification of a process first used in 1883.

3.     In the old process  H₂S was reacted over a catalyst with air to form elemental Sulphur & water.

1.2 AVAILABLE FROMS OF SULPHUR IN CRUDE :

1.      Mercaptans

2.      Sulphones

3.      Sulfides

4.      Disulfides

5.      Sulphoxides

6.      Thiophenes

7.      Sulphates

8.      Sulphonates

1.3 PROPERTIES OF SULPHUR:

PHYSICAL :

Atomic no                 :      16

Atomic mass             :      32.06 g /mol

Electronegativity      :      2.5

Density                     :      2.07g /cm ³ @ 20◦C

Boiling point            :      113◦C

Solubility                   :       It is insoluble in water , sparingly soluble              in alcohol and ether, readily soluble in carbon disulphide, chloroform, xylene, acetone , etc

CONDUCTIVITY : Sulphur is anon conductor of heat and electricity. however, a lump of Sulphur when rubbed by dry hand , or with a wool, becomes electrically charged .

  EFFECT OF HEAT : when heated, Sulphur undergoes a series of changes like evaporation .

CHEMICAL PROPERTIES:

1.     Sulphur exhibits oxidation numbers of -2,0,+2,+4 and +6

2.     Chemical properties of Sulphur- with Air or oxygen : When heated in air or oxygen, Sulphur first melts and then burns with a blue flame to form Sulphur dioxide and some traces of Sulphur trioxide.

3.     Sulphur also combines with most other elements. Sometimes it combines with them easily at room temperature. In other cases, if must be heated.

4.      The reaction between magnesium and Sulphur is typical. When the two elements are heated, they combine to form magnesium Sulphur (MgS).

Sulphur also combines with hydrogen gas. The compound formed in this reaction is hydrogen sulfide (H₂S).  Hydrogen sulphide has one of the best known odour of all compounds.  It smell like rotten eggs. Hydrogen sulfide is added to natural gas (methane) used in homes for cooking and heating. Methane is odorless. So the unique smell of hydrogen sulfide makes it easy to know when there is methane leak.

  second part will continue on 14/12/2013....................