The manufacture of soda ash in the Arabian Gulf.pdf

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International Journal of Production Economics, 21 ( 1992 14% 153Elsevier 145

The manufacture of soda ash in the Arabian GulfKM. Wagialla, I.S. Al-Mutaz and M.E. El-DahshanChemical Engineering Department, King Saud University, Riyadh 11421, Saudi Arabia(Received 4 July 199 I ; accepted in revised form 23 October 1991)

AbstractThis paper is concerned with the technical and economic aspects of the soda ash production in the Arabian Gulf. Fivedifferent manufacturing methods are outlined. The two main manufacturing methods (the Solvay and Dual processes)are examined in detail. The technical aspects regarding the raw material quantitative and qualitative requirements, thebattery limits plant production units and utility requirements are specified in each case. A preliminary economic evalua-tion of each of these two processing routs concludes that soda ash production by either route is competitive with imported

soda ash assuming full marketability of soda ash and its by-products in the Arabian Gulf and neighbouring regions. TheSolvay and Dual processes are estimated to produce soda ash at a cost of 132 and I44 /ton respectively. These productioncosts compare favourably against delivered costs of imported soda ash of 177 /ton.

1. IntroductionSoda ash is the commercial name of the tech-

nical grade sodium carbonate ( Na2C03 ) whichis a white crystalline hygroscopic powder. It is thethird largest chemical manufactured in moderntimes next only to sulfuric acid and ammonia [ 11.It is produced as light or dense soda ash and con-tains 99.3% Na,COj and is graded according toits bulk density and its content of sodium oxide.Dense soda ash is obtained from light soda ashby hydrating it to produce sodium carbonatemonohydrate which is calcined to produce so-dium carbonate (dense soda ash ) :Na2C03 (light) + H,O+Na&O,*H,O

CdC

Na2C03-H,O + Na2C03 (dense) + Hz0About 50% of soda ash (dense grade) producedin the USA in 198 1 was used as a raw material inthe glass industries and 18% in the manufactur-ing of chemicals. Industrial applications of sodaash include paper and paper board, sodium sili-cate, sodium bicarbonate, caustic soda, sodiumnitrite/nitrate, synthetic detergents, sodium sul-phite, sodium thiosulphate, and sodium hydro-sulphite. Large quantities of soda ash are also

used by laundries [ 11. Manufacturing of sodiumbicarbonate and caustic soda are carried out ac-cording to the following two reactions:Na2C03 + Hz0 + C02+2NaHC0,Na,CO,+Ca(OH),+2NaOH+CaCO,2. Manufacturing methods

There are live basic methods for producingsoda ash on a world basis:(i ) By the standard Solvay process (alsoknown as the ammonia soda process) which usessalt ( Na l ) and limestone as basic raw materialsand produces CaCl, as a byproduct.(ii ) By the dual process (or the modified sol-vay process) which uses mainly salt, COz andammonia as raw materials and produces in ad-dition to soda ash the valuable fertilizer com-pound ammonium chloride.

(iii ) By carbonating sodium hydroxide to pro-duce sodium carbonate monohydrate which iscalcined to produce sodium carbonate (densesoda ash ) :2NaOH + C02+Na,COX*H,0

0925-5273/92/ 05.00 0 1992 Elsevier Science Publishers B.V. All rights reserved.


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146The economics of this process depend on theavailability of surplus quantities of NaOH pro-duced as a byproduct of chlorine manufacturefrom brine.

It is interesting to note that the soda ash mar-ket is dependent on the demand for chlorine be-cause during the production of chlorine, causticsoda is also produced which competes in mostapplications with soda ash. Therefore, if thechlorine market grows at a high rate, the result-ing byproduct caustic soda, may take over muchof the soda ash market and depress prices. Thusthe market and feasibility studies for soda ashshould take into account the present and pro-jected caustic/chlorine markets.(iv) From natural Trona deposits. Such de-posits consist largely of Na2C03.NaHC0,.2H,0compounds. It is worth noting that in the USAnatural soda still continues to be the major sourceof soda ash in the USA and in the recent past afew Solvay plants have been shut down becauseof the heavy competitive edge from natural soda[2,31.(v) Recovery from naturally occurring alka-line brines.

Of these five methods the most relevant pro-cesses for the Saudi case are the standard and dualprocesses and these will be described in some de-tail and then compared on a technical and eco-nomic basis.2.1. olvay pr ocess descr i pt i on

In 1861 Ernest Solvay developed the ammo-nia-soda process and hence the name Solvayprocess. It uses salt, limestone and coke or natu-ral gas as raw materials and ammonia as a cyclicreagent. It is based on the fact that ammoniareacts with carbon dioxide and water to formammonium bicarbonate, according to the fol-lowing reactions:NH3+COz+H20+NH4HC03NaCl+ NH4HC0,+NaHC0, + NH&l2NaHCO,+Na,CO, + CO, + HzIn these reactions, the preformed ammonium bi-carbonate reacts with salt to form sodium bicar-bonate. This sodium bicarbonate is then calcined

way(4

(b)(cl

Cd)W

(f-1

to low density soda ash. Chloride is also formedas a byproduct. It is neutralized with lime to formcalcium chloride, as follows:2NH4Cl + Ca (OH ) 2+ CaCl, + 2NH3 + 2H20Almost all the ammonia formed by this reactionis recovered and recycled.

So the raw materials for Solvay process are salt,limestone, and carbon. Ammonia may be con-sidered as a catalyst.The process normally follows the followingsteps.Process description [ 41. The ammonia-soda pro-cess can be summarized according to the follow-ing equation:2NaCl+ CaCO,+Na,CO, + CaCl,However, this chemical reaction is not directlyapplicable. The Solvay process utilizes an inter-mediary stage ( NH4)HC03 in obtaining Na2C03from NaCl and CaC03. The required ammonia( NH3 ) is recycled.This process is summarized in the following

Brine purification, in order to obtain a puresodium chloride solution:Ca++ +C03-tCaC0,Mg+ + +20H+Mg(OH)2Ammonia absorption:2NH,0H+COz-t (NH4)&03+HZ0Carbonation of this ammonia brine afterCO, compression from reactions (e) and(f):NH3+H20+COz-,NH4HC03andNH4HC03 +NaCl+NH,Cl+ NaHC03Filtration of sodium bicarbonate, obtainedunder (c).Decomposition of this bicarbonate intocarbonate, and recovery of COZ:2NaHC03+Na2C03 + HZ0 + CO1Burning of limestone in lime kilns, and CO2recovery:


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(8)

@I

CaCO,+CaO+CO,Lime slaking:CaO+H,0-+Ca(OH)2Ammonia regeneration (distillation):ZNH,Cl+Ca(OH),-+2NH,+CaCl,+Hz0

To summarize, the main raw materials are:brine, which is an aqueous concentrated solu-tion of sodium chloride (N&l ).limestone, which is a calcium carbonate, im-pure CaCO,.ammonia NH3, to compensate the losses dur-ing the process.

Then add:sodium sulfide Na,S, which is a corrosion in-hibitor used in carbonation.fuel oil giving the necessary heat for limestonedecomposition.There is also an important by-product of thisprocess: the distillation sludges, which con-tains calcium chloride CaClz and also excess limeand calcium carbonate. These sludges can be set-tled and the purified liquid used for milk of lime

to supplement step (g) above.Sludges from brine purification and variouseffluents are added to these thickened sludgeswhich are usually stored in a pond.In the salt preparation and purification step,impurities such as calcium sulfate, magnesium,

and iron salts are removed. At this step, specialpretreatments of brine with lime and soda are re-quired as well as precipitation with ammonia andordinary settling. The purified brine then goes tothe second step, the ammoniation step. Brine ab-TABLE I

Light soda Heavy sodaNa2C0, 99.1% min. 99.1% min.NaCl 0.5% max. 0.5% min.Na,SO, 0.04% 0.04%Fe203 0.004% 0.004%H~O/insoluble 0.02% 0.02%Bulk density 0.52 t/m3 1 O t/m3Screen analysis (Tyler) + N 16negligible-No 100 10% max.

147sorbes the necessary ammonia and is then settledand cooled to 25 C and pumped to the carbona-tion towers. The carbonation towers act as theheart of the Solvay process. Sodium bicarbonateis formed by absorption of carbon dioxide inthose towers. The crude sodium bicarbonate iswashed and filtered on a rotary open-drum filter,then it is drawn to the drying or calcination step.A steam-heated calciner is widely used. The pro-duced soda ash from the calciner is then cooledand screened.The economic advantages of the Solvay pro-cess depend on the efficiency of ammonia recov-ery. A good economic process requires the addi-tion of a low amount of ammonia. It utilizes theammonia fed initially in a cyclic path with fewlosses. The ammonia recovery process usuallytakes place in distillation columns.The clarified liquor is further concentrated un-til the molten mass solidifies on cooling givingwhat is known as 75% calcium chloride, corre-sponding to the formula CaCl*-2H 3. Anhy-drous calcium chloride can be made by heatingthis 75% CaCl, when some CaCl? is decomposedgiving Ca and HCl. The scape of this HCl gasleaves a porous mass of fused CaCl, which isknown as 95% CaCl,. CaCl, solution is used asbrine in the manufacture of ice and as an anti-freeze solution, and 75% solid is used as a dustlayer to minimize dust on public highways.Product specifications. The product specifica-tions achieved by the Solvay and Dual processesare essentially the same, see Table 1. This isknown as 58% ash containing about 58% NazO.Excess of insoluble matter will cause cloudinessin soda solution. Excessive iron content will dis-colour the ash rendering it reddish.Typical salt analysis. See Table 2.See Fig. 1 for a complete flow diagram of theSolvay process [ 5 1.2.2. ual process

This is a modified Solvay process. It came incommercial use in 1980. Two impo~ant prod-ucts, soda ash and ammonium chloride are pro-duced. This process provides a substantial savein the amount of salt used. It also does not re-


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148TABLE 2Temperature 25 C

Brine (optimum ) Salt(maximum )

NaCl 310 kg/m7Ca+ + I .6%Mg+ + 0.31%so, 3.70%K- 1.85%Nonsoluble/water 0.3%HumidityLiquid ammonia (standard quality)

99% (dry basis)0.5%0.1%I .2%0.6%0.1%3.0%

NH,OilWaterFeSodium sulphide (standard quality)

99.5% wt. min.10.0 ppm0.5% wt. max.5.0 ppm

Na,SNa&&NaXO,Nonsoluble/waterFe

32.5% crystalNa -9H,O0.3%0.6%0.06%0.01%

Other products. chemicals, operating suppliesH>SO, 98.5% wt. min.HCI 32.0% wt. min.NaOH 50.0% wt.Chemicals for water treatmentChemicals for feed water and boiler waterReagents and chemicals for laboratoryConsumable productsBags for soda ash bagging

quire limestone, an important raw material usedin the classical Solvay process.The principal operation change offered by thedual process is mainly the treatment of the am-monium chloride formed according to the fol-lowing reaction:NaCl + NH4 + CO, + H20+NaHC03 + NH&lIn the Solvay process ammonia is recovered (andrecycled) as suggested by the following reaction:2NH4C1 + Ca ( OH ) z -+CaCl, + 2Hz0 + 2NH3In the dual process, ammonium chloride is re-tained and crystallized out and separated by theaddition of sodium chloride.

In both processes, the sodium bicarbonate iscalcined, soda ash is then formed as follows:2NaHC0,+Na2COX+C0,+H,0The dual process can be summarized by the fol-lowing steps:(1)

(2)

(3)

(4)(5)(6)

Salt washing with purified brine and re-moval of calcium and magnesium ions, asfollowsC+++Na,C03+CaC0,+2Na+Mg++ +2NaOH-+Mg(OH),+2Na+Ammonia absorptionNH,+H20+NH,0H2NH,OH + CO*+ (NH4) &03 + H>OCarbonation of the ammonia brine andproduction of sodium bicarbonate and am-monium chloride

+2NH4HC03 (NH,) HC03 + NaCl--t NaHCO, + NH4C1

Filtration of sodium bicarbonateCrystallization and separation of ammo-nium chloride.Decomposition of bicarbonate into soda ashand recovery of carbon dioxide2NaHC03+NazC03+H,0+C0,

See Fig. 2 for full drawing of the process [ 41.2.3. Raw materials

The main raw materials areRock salt, sodium chlorideAmmoniaco1Sea waterAn examination of the dual process reveals thefollowing features of the process in comparisonwith the standard Solvay process [ 1,2 ] :( 1) High quality fertilizer NH,Cl ) is pro-duced as a coproduct with low salt content whilethe standard Solvay process produces as byprod-uct the relatively less valuable byproduct CaCl,.(2) The soda ash produced has a higher den-sity compared with the product from the Solvay


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149

I r lGhT _WATERLKHT ASH T COOLER SOOA ASH

1Fig. 1.The Solvay process.process, thus requiring less bagging cost.

(3) The process does not require purified saltor a separate brine purification plant as it puri-ties the brine in process.

(4 ) Total elimination of cooling surfaces incontact with process liquor in the process crys-tallization. Thus avoiding shut down of the plantsfor cleaning of heat transfer surfaces.

(5) Use of steam ejectors for cooling. Steamejectors are cheap, can utilize low pressure steam,have no moving parts and are easy to operate.(6) Reaction with CO1 takes place in low costcarbonator units instead of the expensive Solvaycarbonating towers.

(7 ) Use of higher purity CO, results in smallercompressors and lower power consumption.

In fact the dual process for the manufacture ofsoda ash and ammonium chloride basically dif-fers from the Solvay process in the treatment ofthe mother liquor after the precipitation of so-dium bicarbonate. In the standard Solvay pro-cess mother liquor is treated with milk of limeand heated to recover ammonia whereas in thedual process the mother liquor is treated, undercontrolled conditions after addition of ammoniaand salt to precipitate ammonium chloride. Thusin the standard Solvay process, there is regener-ation of ammonia by destruction of ammoniumchloride, in the dual process there is productionof ammonium chloride [ 21. It is worth notingthat ammonium chloride is a commercial prod-

-A

uct in its own right and hence the name dualprocess.3. Project economic evaluation

In this section we will make a preliminary eco-nomic evaluation in order to compare the rela-tive profitability of the two competing techno-logical alternatives; the Solvay and dualprocesses. The third alternative, namely the car-bonation of caustic soda, remains a viable alter-native but unfortunately not enough economicdata were available to us to facilitate the linan-cial evaluation of the process. It is worth noting,however, that a recent preliminary study madeby a local investment corporation estimates theproduct cost of soda ash by the NaOH carbora-tion route in Jubail to be 17 1 /ton (Assuming aunit price of 50% NaOH to be 170 /ton. )Project definition. The foreseen project will havethe following basis:Production capacity: 200000 MT/yearProduct specification:

120000 MT/year light soda ash80000 MT/year heavy soda ashLocation: Al Jubail (Saudi Arabia)Time: First half of 1990Utilities costs.Cooling water (seawater)Steam 1.90 /m34.60 /MT


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15

-aFILTRATION

-

iCOOLING

I

Fig. 2. The dual process.TABLE 3Breakdown of total capital investment of soda ash plant (Solvay process), Design capacity= 200,000 MT/yearDirect costs 000 Indirect cost 000Purchased equipment (delivered)Purchased equipment installationInstrumentation&controlsPipingElectrical equipmentBuildings (including services)

Fixed capital investment 140,943Working capital 24 872Total capital investment,8 i 5

55,10014,8923,8068,2731,65519,939

Spare parts 3,640Engineering 81 supervision 18,367Training & technical assistance 1,820Contractors fees (2% of direct costs) 2,073Contingency (8% of direct & indirect cost) 11,378


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151TABLE 4Raw material and utility requirements per ton of soda ash (Solvay process)Raw materials and chemicals UtilitiesLimestone ( 15 /ton) 1.35 on/TSalt (20 /ton) I .65 ton/TAmmonia (110 /ton) 5.0 Kg/TNazS 3.0 Kg/TSodium carbonate 30.0 Kg/TLime 7.5 Kg/T

TABLE 5Manufacturing cost estimateDirect production costsRaw materialsOperating labourUtilitiesMaintenance and repairsOperating suppliesLaboratory chargesFixed charges

/ton38.818.047.0

6.330.631.9

DepreciationTaxes and insurancePlant overhead costsGeneral expenses

46.9813.8720.0

Administrative costs 3.0Byproduct credits* ( CaCIZ) (65.0)Total product cost 131.51*Estimated CaCI, price (plant gate) is 65 /ton.

Process waterElectricity (from localgrid )Inert gasNatural gasFuel oil

80.0 /m1.5 /kwh1.1 /Nm3

47.0 Q/Gigajoule80.0 /Ton

Scope of cost estimates. The plant location is theindustrial area in Al Jubail. For this reason thecost estimates exclude the costs of dock facilities,sea water (for cooling purposes) and processwater sources, CO, and NH3 plants. Start up,commissioning and infrastructure facilities costsare also excluded.

Fuel oil (for boilers and kiln) 442.0 Kg/TSea water 218.0m/TProcess water 13.0 m/T

Production cost basis.Operating labour [ ( /hr actuallyworked including costs of fringebenefits and 10% shift overlap).Operating supplies (% of operatinglabour)Control laboratory (% of operatinglabour)Plant overhead (% of operating labourplus maintenance labour plus controllaboratory labour)Taxes and insurance (%/year of totalfixed investment ).Alternative A: The Solvay process.

36.4

10%20%

100%

2%

i) The total capital investment. On the basisof a 1982 [ 1 ] cost estimate the purchased equip-ment cost for the main plant and quarry sectionwas 38,786,OOO.Using the appropriate cost indices, the 1990cost of the purchased equipment (delivered plantsite) = 38,786,OOO x 895/630 =55,100,000.On this basis, Table 3 gives a preliminary esti-mate (scope estimate) of the total capital invest-ment which has a probable accuracy estimatewithin ? 20%.

(ii) The total product cost. The raw materialand utility requirements per ton of soda ash(Solvay process) are as estimated in Table 4 [ 4 1.Manufacturing cost estimate. Table 5 shows themanufacturing cost estimate direct productioncost + fixed charges + plant overhead costs) ofthe soda ash plant Solvay process).Alternative B: The dual process also known asthe modified Solvay process ).


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152TABLE 6Breakdown of total capital investment of soda ash plant (dual process), 200,000 MT/yearDirect costsPurchased equipmentPurchased equipment installationInstrumentation & controlsPiping-valves-supportsElectrical equipmentBuildings (including services)

000 Indirect costs54,594 Spare parts21,715 Engineering & supervision4,871 Training and technical assistance10,960 Contractors fee (5% of direct costs)6,494 Contingency (8% of direct & indirect cost)31,051

Fixed capital investment 175,013Working capital 30,885Total capital investment 205,898

0003,836

19,9291,7656,48513,314

TABLE 7

Raw material and utility requirements per ton of soda ash (dual process)Raw materials andchemicals Utilities

Rock salt (20 /ton) 1.2 ton/TCOz (37 /ton) 1.0274 ton/TAmmonia (110 /ton) 0.325 ton/TNazS 3.0 Kg/TSodium carbonate 50.0 Kg/TNaOH 9.5 Kg/T

Electrical power 360.0 KWh/TFuel oil 0.252 Kg/TCooling water 220.0 m3/TProcess water 7.2 m3/T

TABLE 8

Direct product costsRaw materialsOperating labourUtilitiesMaintenance and repairsOperating suppliesLaboratory chargesFixed charges

97.7617.235.531.653.171.81

Depreciation 58.34Taxes and insurance 16.59Plant overhead costs 19.21General expensesAdministration costs 3.0Byproduct credits (NH,Cl)* (140.0)Total product cost 144.23*Estimated NH,Cl price (plant gate) is 140 /ton.

(i) The total capital investment. The produc-tion capacity is 200,000 MT/year of soda ash(60% dense soda ash and 40% light soda ash), inaddition to 200,000 MT/year of ammoniumchloride, see Table 6. The purchased equipmentcost in 1990 (delivered) is estimated to be38,429,OOO x 895/630 = 54,594,OOO.(ii) The total product cost. The raw materialsand utilities requirements per ton of soda ash(dual process) are as estimated in Table 7.Manufacturing cost estimate. Manufacturing cost= direct production cost + fixed charges + plantoverheads, see Table 8.4. Conclusion and discussion

The Solvay and dual processes resulted in sodaash product costs of 13 1.5 1 and 144.23 /ton re-spectively. However, for a preliminary calcula-tion of this nature which has a probable accuracyof +20% these product costs are expected to


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range from 105-l 52 /ton for the Solvay processand 115-l 73 /ton for the dual process. Thequoted prices of soda ash in January 1990 fromUSA were as follows (FOB ) ,

( /ton)58% light 12358% dense 98Since the product mix of the proposed Jubailplant consists of 40% light and 60% dense sodaash, then for comparison purposes we estimatethe price of a hypothetical composite ton of sodaash (0.4 ton light and 0.6 ton dense soda ash)delivered in the Arabian Gulf at 176.5 /ton.This price is well beyond the range of estimatedproduction costs by the two soda ash productionroutes and the outlook for this industry is there-fore encouraging and should be investigatedfurther.However, it should be pointed out quite clearlythat in making these cost estimates the followingunderlying assumptions were made:

( 1) All the soda ash produced (200,000 T/Y)will be marketed either within the Arabian GulfAn allowance of 30 /ton was made for transportation costsfrom west USA to an average Arabian Gulf location.

153countries or in the adjacent Middle Eastcountries.(2 ) The byproducts (calcium chloride in thecase of the Solvay process and ammonium chlo-ride in the case of the dual process) were as-sumed to find market outlets and realize their es-timate prices of 65 /ton and 140 /tonrespectively.In fact the final product costs as calculated inthis study are highly sensitive to the realizedprices of the byproducts. The following tableshows the percentage of byproduct credits anddepreciation charges (the weighted effect of fixedcharges) to the total product cost by either pro-cessing scheme.

Byproduct creditsDepreciation chargesReferences

Solvay49%36%

Dual97%40%

Pandey, R.S. and Mahajan, Y.R., 1982. Modified Solvayprocess and pollution control at PNFC. Chem. Eng. World,19(4): 71-72.Jain, R.C., 1982. Manufacture of soda ash by modifiedSolvay process. Chem. Eng. World, I9 (4): 65-69.Riegel, 1974. Handbook of Industrial Chemistry, 7th edi-tion. Van Nostrand Reinhold, New York.Krebs, 1990. Unpublished data.Faith, W.L., Keyes, D.B. and Clark, R.L., 1965. IndustrialChemicals, 3rd edition. Wiley, New York.

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The manufacture of soda ash in the Arabian Gulf.pdf