Download Centrifugal Pumps for Molten Sulphur & h2so4 Production...
Advances in Materials & Coatings
Centrifugal Pumps for Molten Sulphur and Sulphuric Acid Production Dr. Dr. Jürgn Winrh, Fric-Rhinhü GmbH & Co. KG
To handle and move molten sulphur and sulphuric acid, special pump designs—together with special materials of construction—are necessary to achieve the best reliable solution. Here is an overview of available pump designs and materials for these harsh services. Pumps for Molten Sulphur In recent years, the total world-wide production o sulphur has grown steadily. Sulphur production (Table 1) has been increasingly infuenced by involuntary production o elemental sulphur at gas plants, oil reneries and other hydrocarbon processing operations (recovered sulphur). 1 When transporting sulphur in liquid orm, it is important that the liquid properties are taken into consideration. Abnormal variations variatio ns in viscosity, with changes in temperature, only allow sulphur to be pumped satisactorily in the range o 135-deg C to 155-deg C. For this reason, most pumps used or molten sulphur applications have a heating jacket used to keep the temperature constant in all wetted parts. Also, the content o hydrogen sulphide (H 2S) directly infuences the temperature range, when sulphur can A horizontal pump installation with heating jackets and hydrodynamic shaft seal be pumped with an acceptable viscosity (Figure 1). at a sulphuric acid plant in Uzbekistan.3 There are several alternatives or shat sealing. drive design (e.g. or clean sulphur). Magnetic drive pumps For vertical pumps, stung box packing would be adequate, have the advantage o sae operation without any leakage o while or horizontal pumps hydrodynamic shat sealing, hazardous hydrogen sulphide. mechanical seals or magnetic drive arrangements are recomThe design o vertical pumps depends not only on the mended. purity o sulphur, but also on the size o the sulphur tank or Although vertical pumps are widely used on sulphur meltvessel. For example, cantilever pumps are limited in their subing plants, it is not uncommon to use various designs o horimergence depth. For clean sulphur, single or multistage pumps zontal pumps. with oot and intermediate bearings can be used or submerHorizontal pumps or molten sulphur can have a heavygence depths o up to 17-m. duty design with hydrodynamic shat sealing (e.g. or molten For applications with impure sulphur, the solid size, hardsulphur containing solids), or modern heavy-duty magnetic ness and concentration infuence pump design. Sleeve bearings 52 May 2006
www.pmp-zon.com
PuMPs & systeMs
in hardened material, with internal product lubrication or with external grease lubrication or cantilever pumps, oer a suitable solution or such applications.
Heatable Magnetic Drive Pumps
Table 1 1 World Sulphur Production 2001 - 2004 (million tonnes S/S-equivalent) 2001
2002
2003
2004
Total Production
64.2
64.9
66.9
69.8
Recovered Elemental
40.9
41.8
43.4
45.6
A modern pumping solution or molten Sulphur (in other 16.5 16.7 16.9 forms) sulphur applications are heatable magnetic 57.4 58.5 61.3 Total Involuntary driven pumps, which have zero leakage Mined Elemental 1.3 1.1 0.9 and easy maintenance. 5.5 5.3 5.7 Zero leakage is especially important Pyrites or recovered sulphur, which contains Total Voluntary 6.8 6.4 6.6 mostly H2S gas that should not come into contact with the atmosphere. Pumps with a mechanical seal always have some sulphur leakage, since it is required to lubricate the seal aces. Oten this leakage can be seen in the mechanical seal area as solid sulphur. Heatable magnetic driven pumps have been used or molten sulphur applications or ten years with very good results. Due to the nature o sulphur, these pumps use a special design. In the magnetic coupling / isolation area, a good heat exchange is required in order to dissipate the heat caused by magnetic losses. The sleeve bearing is manuactured with erosion-resistant silicon carbide and it has intensive lubrication that also allows operation at lower capacities. Figure 1. Viscosity of sulphur and inuence of H2S on the viscosity.2 However, the pump has a denite minimum allowable fow rate in order to avoid heat generation inside. The intensive heating area around the pump casing and around the isolation area ensures a constant temperature during operation and a sae start-up. With the jacketed volute casing drain, the pump can be saely emptied without the risk o sulphur crystallization ater pump shut-o.
17.7 63.3 0.8 5.7 6.5
Heavy Duty Horizontal Heatable Pumps with Hydrodynamic Shaft Seal Hydrodynamic shat seals have been used or over 75 years as a means o creating a seal without contact or wear during operation. During operation, the main impeller back vanes work in conjunction with one or more auxiliary impellers to hydrodynamically relieve the pump stung box completely rom pump suction and dierential pressure. In addition, solids are kept away rom the shat sealing area. This pump design
PuMPs & systeMs
Figure 2. Heatable magnetic drive pump.3
works best under permanent operation at a xed speed with steady suction pressure.
www.pmp-zon.com
May 2006
53
Advances in Materials & Coatings Vertical Sulphur Pumps Horizontal pumps cannot be installed in sulphur tanks / pits below ground level. Suitable vertical pumps must be considered. Dierent designs o vertical pumps are available. For recovered sulphur, pumps with shat support bearings are suitable. Submergence depths longer than 2000-mm require additional intermediate bearings. The vertical shat is supported by anti-riction bearings on the top, outside the tank and by sleeve bearings below the mounting fange. The sleeve bearings are lubricated by the sulphur. It is recommended that the maximum pump speed o vertical sulphur pumps is limited to 1500-rpm at 50-Hz or 1800-rpm at 60-Hz, to reduce the risk o temperature rise in the sleeve bearings. Radial orces and pump vibration can Figure 3. Heavy duty horizontal heatable pumps with hydrodynamic shaft seal.3 be limited. The special design eature o vertical molten sulphur pumps is the heating jacket on the unit also requires only a very small opening in the tank/pit. In discharge bend, shat and discharge pipe. addition, all pumps have a double volute casing, which reduces Certain vertical pumps (Figure 4) have some additional radial orces to a minimum. This results in low wear o sleeve design eatures. Some can have up to three stages, which allow a bearings, which increases the MTBF or these pumps. high dierential head at low speed. The discharge and the shat Materials or molten sulphur pumps vary rom cast iron, column are built as a complete unit to give optimum stabilcast steel and stainless steel depending on the application. ity, especially or pumps longer than 2000-mm. This complete
Figure 4. Vertical sulphur pump with steam jackets and one intermediate bearing.3
enter 156 at psfreeinfo.com for more info
54 May 2006
www.pmp-zon.com
PuMPs & systeMs
Pumps for Sulphuric Acid
Table 2: Global Sulphuric Acid Balances, 2004, 2009 and 2014 (million tonnes H 2SO4)
1
Spiritus Vitrioli is the ancient name alchemists used when reerring to the Change 2004 2009 2014 type o etching liquid now known as 04 - 14 sulphuric acid. Initially they produced Production 185.0 222.3 249.7 +64.7 this acid rom alum, but later by burn116.5 140.6 162.6 +46.1 Sulphur ing sulphur with salpeter. 46.3 62.7 70.3 +23.9 Smelter gas Today, sulphuric acid is produced 16.7 12.1 9.6 -7.1 Pyrites rom pyrites, rom other metal sulphides, or rom gases containing sulphur, the 5.5 6.8 7.3 +1.8 Other principal source however being pure sul- Recycled acid 2.5 2.6 2.6 +0.1 phur. Sulphuric acid is reckoned among Supply 187.6 224.8 252.3 +64.8 the most important basic substances o 187.6 224.8 252.3 +64.8 chemical technology and is used in large Demand quantities especially by the industrial 91.4 101.4 110.5 +19.0 Phosphoric acid nations o the world. 96.1 123.5 141.9 +45.7 Other uses It is not without reason that the magnitude o sulphuric acid production iary and decomposition agent in many branches o industry. It is taken as a measure o a country’s state o development. The is used in the production o ertilizers, synthetic washing agents world’s annual production o sulphuric acid is more than 185 and explosives, and is also used in large quantities in the paper, million tons (Table 2). ber, plastics and the metals industry. Although the technology used in sulphuric acid producSulphuric acid does not always remain as a true reaction tion may be viewed as ully developed, one is still, as beore, agent in the nal product, but as a result o contamination trying to improve the methods by increasing the yield and by turns into a residuary acid. Today, ater suitable treatment, this increased use o the heat produced in the process. acid is increasingly recycled into the process. As a result o strict environment laws new ways o producUp to medium concentration, sulphuric acid is almost ing sulphuric acid were invented, e.g. by thermal dissociation dissociated into ions. The aggressivity o the acid is thereore o waste acids, by suitable reconditioning o sulphur containing increased at concentrations between 20 percent to 80 percent. waste gases, or by the use o sulphur containing minerals. At higher concentrations, the dissociation is reduced and the The concentration and partial pressure o the reaction acid thereore becomes less aggressive. components are decisive actors or the conversion. Based on The speed o corrosion o metallic materials in sulphuric the principle o mass action, the company Bayer Leverkusen acid is a unction o temperature, concentration and fow velocinvented the so-called double catalysis process (DP 1136988 ity. The presence o salts, gases or solids can aect the aggresGerman Patent) at the start o the 1960s. siveness o the acid immensely. In this process, 90 percent o the SO 2 is converted into Figure 5 below shows to what extent the concentration, SO3 initially beore primary absorption. The remaining gas is temperature and velocity o sulphuric acid alter the erosion/ again converted in the catalysis, thus increasing the conversion corrosion rate o an austenitic chromium-nickel steel. rate rom 90 percent to 99.5 percent, or even higher, beore In a sulphuric acid plant, vertical and horizontal centriunal absorption takes place. In a heat recovery system, developed by a large company, the heat released by the exothermic reaction in sulphuric acid plants can be utilized or the generation o steam at 10 bar pressure. For the design o circulation pumps at the ront end o the tower, materials that have to withstand concentrated sulphuric acid (99 percent) at temperatures o up to 240-deg C are required. For these applications, suitable alloys are required which oer the highest corrosion resistance, even against erosion corrosion. The same, o course, applies to any other sulphuric acid plants equipped with energy saving heat recovery systems. Figure 5. The effect of velocity and temperature on the corrosion rate of 18/8 Sulphuric acid is used as an important auxil(percent) chromium/nickel steels
PuMPs & systeMs
www.pmp-zon.com
May 2006
55
Advances in Materials & Coatings gal pumps are used to transport diluted and concentrated acids that, apart rom SO2 and SO3, can also contain solids. By selecting suitable resistant materials and pump designs that match the particular process conditions, the high demands made on the pump can certainly be met. Standard materials can only withstand the enormous corrosion and erosion corrosion to a limited extent. Erosion corrosion, which occurs requently, particularly in centriugal pumps is caused by the interaction o liquid ow and powerul turbulence, as well as chemical eects. I a material o sufcient resistance is not used, or worse, i the pump is operated too ar rom its best efciency point, the eect o this intensive type o erosion corrosion can very quickly lead to the destruction o the pump. The lie-time o a centriugal pump is thereore not only dependent on the material used, but also on the way the pump is operated.
Horizontal Pumps for Sulphuric Acid Service For sulphuric acid, horizontal pumps with dierent sealing systems are available. The appropriate system depends on the duty point, the acid properties and the temperature o the application. Sometimes the available and suitable material o construction or a pump component limits the use o a certain
Figure 6. Horizontal Siguss pump with cast iron armour and hydodynamic shaft seal.3
seal design (e.g. spacer can or magnetic drive pump). A highly corrosion-resistant chromium alloy silicon cast iron, called Siguss, has been developed. It has good resistance to wear and increased chemical resistance. This material is chemically resistant to H 2SO4 at all concentrations up to boiling point, thereore suitable or all sulphuric acid applications including the evaporation o waste acid. Due to the brittleness o the material, a special armored
Global Petroleum Show 2006
June 13 - 15, 2006 Stampede Park, Calgary, Canada The world’s largest oil and gas event. • • • • • •
Microsoft Technology Pavilion - NEW! GPS Speaker Series - NEW! GPS Keynote Luncheons - NEW! Over 50,000 registered delegates from 85 countries Over 1,500 exhibiting companies Over 130 acres of displays and equipment
Register online at
Because technology changes everything. Major exposition sponsors HALLIBURTON
For your free, personalized entry pass, register online at www.petroleumshow.com - SAVE $80 enter 114 at psfreeinfo.com for more info
56
May 2006
www.pmp-zon.com
PuMPs & systeMs
pump design is required (Figure 6). This material can only be used or horizontal pumps.
Vertical Pumps for Sulphuric Acid Service Typical sulphuric acid plants are equipped with vertical pumps throughout the various stages o the process (drying tower, primary and secondary absorption tower and oleum tower). Depending on the actual location o the pump in the process, dierent Figure 7. Vertical acid circulation materials will be required pump.3 to withstand acid concentrations and temperatures. Each pump manuacturer has their own materials developed or these special requirements. Figure 7 shows a typical vertical acid circulation pump. Slight changes in acid concentration and/or temperature
can result in serious equipment damage. Figure 8 shows a damaged pump impeller. Pumps or these type o applications require a high level o engineering. Pump manuacturers should be consulted to nd Figure 8. Damaged pump impeller.3 the most reliable solution regarding design, materials o contruction, sealing systems and pump operation. P&S Footnotes: 1
M. Kitto, World Sulphuric Acid Situation, British Sulphur Consultants, Sulphur 2005, Moscow. 2 Douglas K. Louie, Handbook o Sulphuric Acid Manuacturing, DKL Engineering, Inc. Ontario, 2005. 3 Friatec-Rheinhuette GmbH & Co. KG, Wiesbaden, Germany.
Dr. Jürgen Weinerth can be contacted at FRIATEC-Rheinhütte GmbH & Co. KG, Rheingaustr. 96-98, Wiesbaden, 65203, Germany, +49 (0) (611) 6040, Fax: +49 (0) (611) 60432, www.rheinhuette.de,
[email protected].
enter 134 at psfreeinfo.com for more info PuMPs & systeMs
www.pmp-zon.com
May 2006
57
