Sulfur Recovery Units (SRU)

Sulfur Recovery Units (SRU) 1. Proses Claus Proses Claus merupakan proses kimia katalitik yang dimanfaatkan untuk mengkonversi gas hydrogen sulfide (H2S) menjadi elemental sulfur (S).Proses ini sering disebut sebagai Sulfur Recovery Unit (SRU) dan sangat sering digunakan untuk menghasilkan sulfur dari hydrogen sulfide yang terdapat pada gas alam mentah dan sour gas yang mengandung hydrogen sulfide yang berasal dari pengilangan minyak bumi, minyak mentah dan [1] fasilitas industry lainnya. Deskripsi proses :

[2]

The basic Claus unit comprises a thermal stage and two stage or three catalyst stages. Typical sulfur recoveries efficiencies are in the range 95-98% depending upon the feed gas composition and plant configuration. The basic chemical reactions occurring in a Claus process are represented by the following reactions :

   ⁄           ⁄    

Some of the H2S in the feed gas is thermally converted to SO2 in the reaction furnace of the hermal stage according to reaction (1). The remaining H2S is then reacted with the thermally produced SO2  to form elemental sulphur in the thermal stage and the subsequent catalytic stages according to reaction (2). Claus reaction (2) is thermodynamically limited and has a relatively low equilibrium constant for reaction (2) over the catalytic operation region. As the feed acid gas normally contains other compounds, which could include carbon dioxid, hydrocarbons, mercaptants and ammonia, the actual chemistry in the furnace is very complex. The latest analysis of this has been presented by Borsboom and Clark.

Simplified Process Description o  The hot combustion products from the furnace at 100-1300 C enter the waste heat  boiler and are partially cooled by generating steam. Any steam level from 3 to 45 bar g can be generated  The combustion products are further cooled in the sulphur condenser, usually by generating LP steam at 3-5 bar g. This cools the gas enough to condense the sulphur formed in the furnace, which is then separated from the gas and drained to a collection pit.  In order to avoid sulphur condensing in the downstream catalyst bed, the gas leaving the sulphur condenser must be heated before entering the reactor.  The heated stream enters the first reactor, containing a bed of sulphur conversion catalyst. About 70% of the remaining H2S and SO2  in the gas will react to form sulphur, which leaves the reactor with the gas as sulphur vapour.  The hot gas leaving the first reactor is cooled in the second sulphur condenser, where LP steam is again produced and the sulphur formed in the reactor is condensed  A further one or two more heating, reaction, and condensing stages follow to react most of the remaining H2S and SO2  The sulphur plant tail gas is routed either to a Tail Gas treatment Unit for further  processing, or to a Thermal Oxidiser to incinerate all the sulphur compounds in the tail gas to SO2 before dispersing the effluent to the atmosphere.

2. Proses LO-CAT Proses LO-CAT bersifat aqueous  (basah), bertemparatur rendah yang menggunakan regenerasi katalis besi. Katalis besi digunakan untuk mengkonversi hydrogen sulfide menjadi unsur yang tidak berbahaya, sulfur. Proses ini tidak menggunakan bahan kimia  beracun dan tidak menghasilkan produk sampingan berupa limbah berbahaya. Katalis yang tersedia akan terus mengalami regenerasi dalam proses, sehingga penggunaan [1] katalis lebih sedikit dan penghematan juga dilakukan. [1] Deskripsi proses : Intensitas proses adalah mengoksidasi ion-ion hydrosulfide (HS ) menjadi unsur sulfur 3+ 2+ dengan mereduksi ion ferik (Fe ) menjadi ion ferrous (Fe ) dan tahapan reoksidasi ion ferrous menjadi ferik melalui kontak dengan udara. Proses kimia adalah sebagai berikut : Absorpsi H2S

()   ()   ()   () Ionisasi H2S

 ()      Oksidasi Sulfida

              Absorpsi Oksigen

⁄    ()  ⁄   ()  ()  ()

Oksidasi Besi

   ⁄ ()        Reaksi keseluruhan

 ()  ⁄  ()     

TM

3. Shell-Paques/THIOPAQ TM Proses Shell-Paques/THIOPAQ dapat menghilangkan H2S pada aliran gas alam tekanan rendah, sedang ataupun tinggi. Pada proses ini aliran gas yang mengandung H2S dikontakkan dengan larutan air soda yang mengandung bakteri Thiobacillus  pada absorber. Soda mengabsorp H2S dan sialirkan ke aerated atmospheric tank  dimana secara [1]  biologi bakteri mengubah H2S menjadi sulfur. [1] Deskripsi proses : Reaksi yang terjadi di absorber (pada tekanan feed gas)

                                 Reaksi yang terjadi di bioreactor (pada tekan an atmosfer)

   ⁄  ⁄                              Note : (tambahan tentang Proses Claus) [3] This process includes two main section : the burner section with a reaction chamber that does not have a catalyst, and a Claus reactor section. In the burner section, part of the feed containing hydrogen sulfide and some hydrocarbons is burned with a limited amount of air. The two main reactions that occur in this section are the complete oxidation of part of the hydrogen sulfide (feed) to sulfur dioxide and water and the partial oxidation of another part of the hydrogen sulfide to sulfur. The two reactions are exothermic :

   ⁄          ⁄   ⁄    

             

In the second section, unconverted hydrogen sulfide reacts with the produced sulfur dioxide over a bauxite catalyst in the Claus reactor. Normally more than one reactor is available. In the Super-Claus process (Figure 4-3), three reactors are used. The last reactor contains a selective oxidation catalyst of high efficiency. The reaction is slightly exothermic :

      ⁄    

      

Figure 4-3. The Super Claus process for producing sulfur. (1) main burner, (2,4,6,8) condensers, (3,5) Claus reactors, (7) reactor with selective oxidation catalyst After each reaction stage, sulfur is removed by condensation so that it does not collect on the catalyst. The temperature in the catalyst converter should be kept over the dew point of sulfur to prevent condensation on the catalyst, which reduces activity. Due to the presence of hydrocarbons in the gas feed to the burner section, some undesirable reaction occur, such as the formation of carbon disulfide (CS2) and carbonyl sulfide (COS). A good catalyst has a high activity toward H 2S conversion to sulfur and reconversion of COS and CS2  to sulfur and carbon oxides. Mercaptans in the acid gas feed results in an increase in the air demand. For example, approximately 5-13% increase in the air required is anticipated if about 2 mol% mercaptans are present. The increase in the air requirement is essentially a fuction of the type of mercaptans present. The oxidation of mercaptans could be represented as:

               ⁄        

Sulfur dioxide is then reduced in the Claus Reactor to elemental sulfur. REFERENCES : 1. Hidayat, Sungging. 2012. “Perancangan dan Estimasi Biaya Sulfur Recovery Unit  metode Superclaus”. Fakultas Teknik Departemen Teknik Kimia, Universitas Indonesia, Depok.

2. Mahin Rameshni, P.E “Sulfur Recovery Unit : Expansion Case Studies” Worley Parsons, resources & energy, UK 3. Sammi Matar and Lewis F. Hatch.1994.”Chemistry of Petrochemical Processes second edition; provides quick and easy access to hundreds of reaction, processes and products”, Texas. Hal 116-117 4.