Pumps for Sodium Hydroxide Service

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Engineering Design Guide: GBHE_EDG_MAC_1514

Pumps for Sodium Hydroxide Service

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Information contained in this publication or as otherwise supplied to Users is believed to be accurate and correct at time of going to press, and is given in good faith, but it is for the User to satisfy itself of the suitability of the information for its own particular purpose. GBHE gives no warranty as to the fitness of this information for any particular purpose and any implied warranty or condition (statutory or otherwise) is excluded except to the extent that exclusion is prevented by law. GBHE accepts no liability resulting from reliance on this information. Freedom under Patent, Copyright and Designs cannot be assumed.



Engineering Design Guide: Pumps for Sodium Hydroxide Service

CONTENTS 1 SCOPE 2 PROPERTIES OF FLUID 2.1 General Properties of Sodium Hydroxide 2.2 Physical Properties of Sodium Hydroxide and its Solutions 2.3 Chemical Properties and uses of Sodium Hydroxide 2.4 Physiological effects of Sodium Hydroxide 2.5 Specifications of Commercial Caustic Soda Grades 3 CHOICE OF PUMP TYPE 3.1 Pump Duty 3.2 Pump Type

4 RECOMMENDED LINE DIAGRAMS 5 RECOMMENDED LAYOUT 6 CONSTRUCTION FEATURES 7 MATERIALS OF CONSTRUCTION 7.1 Nickel and Nickel Alloys 7.2 Austenitic Stainless Steel 7.3 Aluminium, Aluminium Alloys, etc. 7.4 Non-Metallic Materials



TABLES 1 PHYSICAL PROPERTIES (Solid Form) 2 PHYSICAL PROPERTIES (Solution Form) 3 CAUSTIC SODA GRADES FIGURES 1.1 LINE DIAGRAM - HORIZONTAL GLANDED, GLANDLESS AND

VERTICAL IN-LINE PUMPS 1.2 LINE DIAGRAM - VERTICAL SPINDLE CANTILEVER PUMPS 1.3 LINE DIAGRAM - SELF PRIMING PUMPS 1.4 LINE DIAGRAM - RECIPROCATING PLUNGER METERING PUMPS 1.5 LINE DIAGRAM - POSITIVE DISPLACEMENT DIAPHRAGM

METERING PUMPS 1.6 WATER FLUSHING ARRANGEMENT FOR DOUBLE MECHANICAL

SEAL 1.7 WATER FLUSH (QUENCH) ARRANGEMENT FOR SINGLE HARD

FACED (CARBIDE) SEAL AND BACK-UP LIP SEAL 2 PHASE DIAGRAM OF NaOH-H2O 3 VISCOSITY OF AQUEOUS CAUSTIC SODA SOLUTIONS 4 VAPOR PRESSURE OF AQUEOUS CAUSTIC SODA SOLUTIONS 5 ENTHALPY CONCENTRATION FOR AQUEOUS CAUSTIC SODA

SOLUTIONS



6 SPECIFIC GRAVITY FOR AQUEOUS CAUSTIC SODA SOLUTIONS 7 DILUTION OF CAUSTIC SODA LIQUOR 8 THERMAL CONDUCTIVITY OF AQUEOUS CAUSTIC SODA

SOLUTIONS 9 SPECIFIC HEAT OF CAUSTIC SODA SOLUTIONS 10 BOILING POINTS OF STRONG CAUSTIC SODA SOLUTIONS

AT REDUCED PRESSURE 11 COMMENCEMENT OF FREEZING OF CAUSTIC SODA SOLUTIONS

(0 - 52% W/W) 12 TEMPERATURES ATTAINED ON DISSOLUTION OF ANHYDROUS

CAUSTIC SODA 13 HEAT OF SOLUTION FOR ANHYDROUS CAUSTIC SODA 14 SOLUBILITY OF SODIUM CHLORIDE IN CAUSTIC SODA SOLUTIONS 15 DENSITY - CONCENTRATION TABLES FOR CAUSTIC SODA

SOLUTIONS AT 600 F (15.5 0 C) 16 MATERIAL SELECTION CHART FOR CAUSTIC SODA HANDLING DOCUMENTS REFERRED TO IN THIS ENGINEERING DESIGN GUIDE



1 SCOPE

This Engineering Design Guide provides guidance on the selection of suitable pumps for pumping Sodium Hydroxide and its various aqueous solutions.

2 PROPERTIES OF FLUID 2.1 General Properties of Sodium Hydroxide

Sodium hydroxide is commonly called caustic soda within industry. It is generally handled in solution form at varying strengths from 6% to 100% caustic soda. The physical properties of the solutions vary with the caustic strength as shown in 2.2 which summarizes the properties for the most common solution strengths.

The 100o Twaddell (47% w/w) caustic soda liquor is the most common solution as it is both easy and economical to distribute and in this form it is an almost colorless liquid, being quite viscous and dense. It is miscible with water in all proportions below this value and the commencement of freezing varies dramatically with solution strength.

100% caustic soda is a solid at room temperature.

2.2 Physical Properties of Sodium Hydroxide and its Solutions

Chemical formula NaOH Molecular weight 40 Melting Point 318o C Sodium hydroxide (100% w/w) has the following additional physical properties: (a) It is a white crystalline solid at ambient conditions. (b) It is very soluble in water giving off a large amount of heat in the

process. (c) It is deliquescent.



(d) It absorbs carbon dioxide from the air. In solid form, the following physical properties apply:

TABLE 1: PHYSICAL PROPERTIES (Solid Form)

In solution form, the-following physical-properties apply: TABLE 2: PHYSICAL PROPERTIES (Solution Form)



The following Figures apply:

Figure 2 Phase diagram of NaOH-H2O

Figure 3 Viscosity of Aqueous Caustic Soda Solutions

Figure 4 Vapor Pressure of Aqueous Caustic Soda Solutions

Figure 5 Enthalpy Concentration for Aqueous Caustic Soda Solutions

Figure 6 Specific Gravity for Aqueous Caustic Soda Solutions

Figure 7 Dilution of Caustic Soda Liquor

Figure 8 Thermal Conductivity of Aqueous Caustic Soda

Solutions

Figure 9 Specific Heat of Caustic Soda Solutions

Figure 10 Boiling Points of Strong Caustic Soda Solutions at Reduced Pressure

Figure 11 Commencement of Freezing of Caustic Soda Solutions (0 - 52% W/W)

Figure 12 Temperatures Attained on Dissolution of Anhydrous

Caustic Soda Figure 13 Heat of Solution for Anhydrous Caustic .Soda Figure 14 Solubility of Sodium Chloride in Caustic Soda

Solutions Figure 15 Density - Concentration Tables for Caustic Soda

Solutions at 60° F (15.5° C) Figure 16 Material Selection Chart for Caustic Soda Handling.



2.3 Chemical Properties and uses of Sodium Hydroxide

Sodium hydroxide is highly corrosive and one of the strongest alkalis in commercial use. It is a very stable compound and cannot be converted into the oxide by heating. Aqueous sodium hydroxide attacks glass, the silica being dissolved as sodium silicate. It also dissolves metallic boron, silicon, aluminium, tin and zinc, liberating hydrogen and forming a sodium salt of the oxide. Copper is more resistant but in the presence of air and especially at temperatures approaching the boiling point of the solutions, sodium hydroxide is readily contaminated by copper. Other metals are attacked by fusion with sodium hydroxide in the presence of air, but nickel and the noble metals are almost unaffected. Some of the non-metals are also dissolved, as oxy-salts, by aqueous sodium hydroxide but with the formation of an hydride (or a salt of the hydride) instead of free hydrogen. On account of its power of emulsifying oils and grease, it is a powerful cleansing agent for machines, sheet metals, etc. It is used to convert fats into "hard" soap, and also in the manufacture of sodium and alkaline bleaching solutions, in the purification of bauxite and as a reagent in the treatment of organic materials such as paper, artificial silk and dyes..

2.4 Physiological Effects of Sodium Hydroxide

If sodium hydroxide touches the skin and is allowed to remain in contact for more than a few seconds, it will destroy the skin, causing a serious chemical burn that will take a long time to heal - and will leave a scar. If it gets into the eye and is allowed to remain for more than a few seconds, it will persistently penetrate and destroy the tissues of the eye - resulting in the loss of the eye or impaired vision due to scaring.

If sodium hydroxide is swallowed, an antidote is required to be taken into the stomach without delay.

(d) Bypass control with the control valve in the bypass line is the normal

regulation method for rotary pumps.



2.5 Specifications of Commercial Caustic Soda Grades TABLE 3: CAUSTIC SODA GRADES



3 CHOICE OF PUMP TYPE 3.1 Pump Duty

The pump duty is determined and the preliminary pump type selected in accordance with GBHE-EDG-MAC-1014.

3.2 Pump Type

(a) For Caustic Soda Strengths up to 50% w/w

For solution strengths up to 50% w/w the preferred type of pump is the horizontal end-suction back pull-out centrifugal pump to BS 5257.

Alternatively glandless horizontal spindle end suction pumps can be used of either magnetic drive or canned motor design, to eliminate seal problems. Normally an inlet strainer would be necessary, particularly if the liquor to be pumped is not clean. "Slurry" type designs are available for glandless pumps but they should only be specified when absolutely necessary. If vertical spindle submerged pumps are required then these shall be of the cantilever type, to eliminate problems associated with intermediate and bottom bearings. For pit/sump duties horizontal spindle self-priming pumps have been used successfully. Vertical in-line pumps have also been used with success, for general sodium hydroxide pumping duties, but these are non-preferred due to the multi-trade nature of any maintenance activities, and the inherent inferior access to seals.

(b) For Caustic Soda Strengths in Range 50% - 100% w/w

Glandless horizontal spindle end suction pumps are recommended. Vertical spindle cantilever pumps can be used for vessel/pit/sump duties.



(c) Positive Displacement Pumps

On certain duties such as filtering, it is necessary to use positive displacement pumps. The helical metallic rotor/double helical resilient stator design (progressive cavity type) is recommended. Lobe pumps have also been used successfully. For pumping weak solutions from effluent pits air-operated double diaphragm pumps have also been used. These have the advantage of being portable, but they are, however, inherently inefficient, and the diaphragm lives are relatively short. In metering applications, plunger Or diaphragm pump-heads are used. The plunger models are specified where very accurate metering is required. Leak tight operation can be obtained by utilizing various combinations of packing or seals. .The diaphragm models are of glandless design and are particularly suited for the more difficult duties, viz strong, hot solutions of caustic soda. NB: Pressure relief bypass valves are required for any design of

positive displacement pump.

4 RECOMMENDED LINE DIAGRAMS

The following line diagrams are typical only, due to the large possible permutations of caustic soda solution strengths, duty temperatures, pump types and seal designs. Figure 1.1 - Horizontal Glanded, Glandless, and Vertical In-line Pumps Figure 1.2 - Vertical Spindle Cantilever Pumps Figure 1.3 - Self Priming Pumps Figure 1.4 - Reciprocating Plunger Metering Pumps Figure 1.5 - Positive Displacement Diaphragm Metering Pumps



Figure 1.6 - Water Flushing Arrangement for Double Mechanical Seal

Figure 1.7 - Water Flush (Quench) Arrangement for Single Hard

Faced (Carbide) Seal and Back-up Lip seal.

5 RECOMMENDED LAYOUT

Pipework should not be run directly above the motor/pump units because of the risk of leakage and external corrosion. The availability of water wash facilities should be provided in the near vicinity. The specification of the bunded area and its integrity should be checked. Foundation bolts which penetrate the tiled or special concrete area shall not be used. Adequate drainage facilities shall be provided to deal with leakage and contaminated wash water. Access to drain plugs or valves should be checked. Additional stop buttons should be located outside the bunded/tiled area away from the pumps. Maintenance access around the units should be checked, together with the adequacy of any lifting/handling facilities.

6 CONSTRUCTION FEATURES

For caustic soda concentrations in the range 0 to 50% w/w, pumps should be heated and lagged. Electric, LP steam or hot water trace heating may be used. For 73% w/w caustic soda liquor, electric or LP steam trace heating should be designed to maintain the liquor in the pump chamber at approximately 100o C at all times. All pumps should have facilities for emptying the pump chambers and for washing out.



Pump glands should be fitted with anti-splash guards, and pumps should be positioned in a suitable catchment tray or area which drains to a sump. The following types of seals can be used: (a) Packed glands. (b) Single mechanical seal/back-up lip seal with low pressure

flush/quench. (c) Double mechanical seal with pressure water flush. For materials of construction see Clause 7. Impellers of centrifugal pumps shall normally be of the shrouded design. However, where solids are likely to be a problem, open or semi-open impellers should be specified.

7 MATERIALS OF CONSTRUCTION

For solutions of caustic soda up to 50% w/w strength, pumps should be all ferrous fitted, e.g. cast iron casing, stainless steel or cast iron impeller, stainless steel or mild steel shaft. Where gland packings are used, these should be asbestos/graphite – Crane style SS6 or equivalent. Where iron and heavy metal contamination of the caustic liquor is forbidden, titanium pump components have been used. It is important to look at the service conditions in detail so as to get the materials selection correct for the particular application. For solutions strengths in the region of 73% w/w, the casing and impeller should be 101A Ni-Resist, and other internals of Inconel 600 Shafts, washers etc. should be Monel 400 and bushes and thrust bearings in carbon grade CY10F. For pumping hot anhydrous caustic soda at about 400o C, the use of commercially pure nickel material is necessary.



Where mechanical seals are to be used, the component materials should be carefully selected with the manufacturer in consultation with Materials Group. A wide range of seal designs and material options are available, and consideration should be given to all components making up the seal, viz, flexible member, rotating face, metal parts, stationary seats and springs etc. For single mechanical seals, tungsten carbide and silicon free silicon carbide has been used successfully for the seal faces - this prevents abrasion of the seal faces by caustic crystal. Carbon steel is the generally accepted material of construction used for caustic soda storage equipment. Solutions containing up to 50% caustic soda are without action on unstressed steel at temperatures up to 40o C. The corrosion rate of mild steel in 50% caustic soda liquor is typically <0.01 to 0.25 mm/yr in the temperature range 50 – 100o C.

7.1 Nickel and Nickel Alloys

Nickel and nickel alloys are among the most resistant materials for handling caustic soda and in decreasing order of resistance are nickel, Inconel, Monel and Incoloy 825. With all but Incoloy 825 contact with sulfur compounds during fabrication can cause cracking, and specialized handling and welding techniques are essential during fabrication. The corrosion rate of nickel and the above alloys in 50% caustic- soda liquor is negligible at temperatures up to 150o C.

7.2 Austenitic Stainless Steel

Austenitic stainless steel containing 18% chromium, 8% nickel, 2.5% molybdenum (AISI types 316, 316L) are resistant to 50% caustic soda solution at temperatures up to about 100o C. The corrosion rate should not exceed 0.001 mm/yr.

7.3 Aluminium, Aluminium Alloys, etc.

Aluminium, aluminium alloys, tin, zinc (galvanizing) - lead and brass are not suitable for use with caustic soda liquors. Aluminium and its alloys react rapidly with caustic solutions to produce hydrogen which in certain circumstances could lead to an explosion hazard.



7.4 Non-Metallic Materials

Non-Metallic Materials - All natural rubbers are resistant to caustic soda solutions over a temperature range up to 80° C. Gaskets for flanged joints should be fabricated from acid, alkali, and heat-resisting rubber jointing to Specification M.228. For higher temperatures butyl rubber should be used. Thermoplastics are satisfactory up to their maximum design temperature depending upon the particular use, e.g. – vessel linings, pipe linings, integral structures with GRP reinforcement etc.

Nylon is only suitable for cold dilute solutions of caustic soda, for instance 10% at room temperature. Soda lime glass is rapidly attacked; Borosilicate glass (Pyrex) is resistant to 50% solutions up to 30o C. Vitreous enamel may be used for cold dilute solutions but is not suitable for strong solutions.

See Figure 16 - Materials Selection Charts for Caustic Soda Handling.



FIGURE 1.1 LINE DIAGRAM - HORIZONTAL GLANDED, GLANDLESS AND VERTICAL IN-LINE PUMPS



FIGURE 1.2 LINE DIAGRAM - VERTICAL SPINDLE CANTILEVER PUMPS



FIGURE 1.3 LINE DIAGRAM - SELF PRIMING PUMPS

NOTE Other possible methods of self priming are: 1 Priming water injection ihto suction line. 2 Suction line priming tank. 3 Manual vacuum priming. 4 Automatic vacuum priming using secondary vacuum system comprising

either a vacuum pump and priming tank or preferably a compressor and ejector.

5 Foot valve (not recommended).



FIGURE 1.4 LINE DIAGRAM - RECIPROCATING PLUNGER METERING PUMPS

FIGURE 1.5 LINE DIAGRAM - POSITIVE DISPLACEMENT DIAPHRAGM

METERING PUMPS



FIGURE 1.6 WATER FLUSHING ARRANGEMENTS FOR DOUBLE MECHANICAL SEAL



FIGURE 1.7 WATER FLUSH (QUENCH) ARRANGEMENT FOR SINGLE HARD FACED (CARBIDE) SEAL AND BACK-UP LIP SEAL



FIGURE 2 PHASE DIAGRAM of NaOH-H2O



FIGURE 3 VISCOSITIES OF AQUEOUS CAUSTIC SODA SOLUTIONS



FIGURE 4 VAPOR PRESSURE OF AQUEOUS CAUSTIC SODA SOLUTIONS



FIGURE 5 ENTHALPY CONCENTRATIONS FOR AQUEOUS CAUSTIC

SODA SOLUTIONS



FIGURE 6 SPECIFIC GRAVITY FOR AQUEOUS CAUSTIC SODA

SOLUTIONS



FIGURE 7 DILUTION OF CAUSTIC SODA LIQUOR



FIGURE 8: THERMAL CONDUCTIVITY OF AQUEOUS CAUSTIC

SODA SOLUTIONS



FIGURE 10 BOILING POINTS OF STRONG CAUSTIC SODA SOLUTIONS

AT REDUCED PRESSURE



FIGURE 11 COMMENCEMENT OF FREEZING OF CAUSTIC SODA

SOLUTIONS (0 - 52% W/W)



FIGURE 12: TEMPERATURES ATTAINED ON DISSOLUTION

OF ANHYDROUS CAUSTIC SODA



FIGURE 15 DENSITY - CONCENTRATION TABLES· FOR CAUSTIC SODA SOLUTIONS AT 60o F (15.5o C)



FIGURE 16 MATERIAL SELECTION CHART FOR CAUSTIC SODA

HANDLING



DOCUMENTS REFERRED TO IN THIS ENGINEERING DESIGN GUIDE This Engineering Design Guide makes reference to the following documents BRITISH STANDARDS BS 5257 Horizontal End-Suction Centrifugal Pumps

(referred to in 3.2) GBHE ENGINEERING DESIGN GUIDES GBHE-EDG-MAC-1014 Integration of Special Purpose Centrifugal

Pumps into a Process (referred to in 3.1)

JOINTING Acid, Alkali and Heat-Resisting Rubber jointing (referred to in 7.4).

Pumps for Sodium Hydroxide Service

Technology

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