processing industrial byproducts to yield as fertilizer

8/12/2019 Processing Industrial Byproducts to Yield as Fertilizer

1/13

CAPProcessing Industrial Byproducts t o YieldAmnonium Sulfate Fertlliter

Michael R Overcash, ProfessorKen Wood, Research AssistantDepartment of Chemical EngineeringNorth Carolina Sta te UniversityRaleigh, North Car olina 27695-7905

EXECUTIVE SUMMARY

The was te minim izati on program in Chemical Engineering at NorthCarolina State University has developed a screening and selection processto identify industrial situations with favorable probabilities forprevention of pollution emissions. The potential util izati on of spentsulfuric acid and b y p r Q d q amnonia to yield amnonlum sulfate fertilizerfrom gk h em i ca l manufacturjr was identified by this screening proc ess as acandidate for a' p r e l - h n a r y engineering assessment. The magnitud e o fammonium sul fate production would be approximately 2,000 tons per year witha annual value between 2,000 and 34,000. In addition, the geographiclocation o thi s industrial plant in western North Carolina match es theregional need for sulfate-based fertilizer.

In thi s report the objec tive s of the overall industry screeningprocess and of the typical preliminary engineering assessment a re given.The pollutio n prevention situation illustrated by this case study is notone of direct reduction of environmental emission since the two byproductstrea ms are currently treated or sold completely. Rather the iss ueinvolved here in is one of potential increased value by the combi natio n oftwo byprod uct streams.

Proces s calculations and overall stoichiometric determinations weremade on the reaction of ammonia gas and sulfuric acid solutions.Considerations of the pH rang e to be used and th e need to cool the react ionin a full-scale operation were evaluated. Some suggestions of reactordesign and innovative means t o achieve a low cost desig n are given. Th edirection o f futur e work is described fo r both engineering pilot stud ies aswell as t he agricultural ev aluat ions which would be appropriate.The industrial concern has expended approximately f 10,000 on thisconcept However factors outside thewaste mini mizat ion considerations have dictated that the ammonium sulfa tewill not be produced. A s is often the case, market conditions change andin this case the need for the product from which ammonia gas was abyproduct has been reduced such that further production was eliminated.The industry has switched to other products. Thus the opportunity for thiswaste minimization i s eliminated. A s a feedback to the overall process by

as well as 3,000 from th is project.


2/13

whlch resources are applled to stlmulate waste ninlmizatlon, thls casestudy descrlbes that whic h may not be uncommon. Not all conc epts developedas means o f pollution preventlon can be implemented since factors outsidethe technical aspects for such waste reduction are also very Important.Thus I t I s important to undertake as much screening and continualre-evaluation to assess both the technical factors and the broaderindustrial setting in which all proces s modifications or recycle/reuse mustbe placed.


3/13

Processing Industrial By products to YieldAmmonium Sulfate Fertilizer

INTRODUCTION

The was te m inimi zatio n program in Chemical Engi neeri ng at NorthCarolina Sta te University is aimed at the research, development,engineering, and implementation for waste minimization in industry. Theprogram is thu s focused on the technical and economic stages necessary toactually implement the lowering of wast e emiss ions from industry. In orderto make significant contributions to the waste minimization field, aselection process has been developed to screen concepts or interests o findustry thro ugh several level s in an attempt to clari fy the actualfeasibility of pollution prevention (Overcash 1986). This iterativescreening process leads to a subset of industrial circumstances in which

a) the emissio n magnitude or value is within a reasonable rangefor probable recovery or elimination

b) the industry comnitment to conside ring a waste minimizationscheme is evident

c) ther e exist critical unavai lable information which the N.C.S.U.program could gener ate by labor atory and pilot-scale s tudies orby detailed engineering analysis and design.

.An intermediate stage in this overall identification and screening processfor waste minimization situations i s a preliminary engineering assessment


4/13

P

of a p r o j e c t .

The object ives of a preliminary engineering assessment often varyamong Industrial projects. The level of curr ently ava ila ble informationand on-going activ ity gre atl y affect the results and level of detail fo rsuch an assessment. Howeve r a number of object ives occ ur routinely i nthese assessments. Thes e are

a) to determine the extent of tangible industry interest inundertaking the variou s stag es toward the elimination orreduct ion of a particular waste stream

b) to begin quantification o f the extent by which chemicals maybe eliminated at individual manufacturing facilities andthe correspo nding preliminary economics

c) to explore the natur e of potential solutions such thatseveral alternative approaches are available to allow f orchange s in manufacturing and transfer to a wide ran ge ofsimilar manufacturing facilities

d) to iden tify the appropri ate next steps toward implementinga potential wa ste minimi zatio n scheme, usually th e initiationof labo rator y or pilot-scale tests aimed at critical missinginformation.

The preliminary engineering ass essment usually involves currently availableinformation supplemented with plant visits and ap propr iate scientificanalysis. The se investi gati ons are aimed at relating prior experienc e with


5/13

Industry and waste mlnlmlzatlon technology to a new circumstance In whichthere appears to be potential and Interest In reducing waste emisslons. Inthis process, the techn ology group at North Carolina State Universityprovides Industry the oppor tunit y to maintain confidentiallty until suchtime as the manufacturing organization decides to allow specificIdentification. There are a number of benefits to industry when directlyidentified with the developmen t of innovative means of reducing wastesproduced. However, technology implementa tion group at N C S U doesextract and disseminate the generic and developmental facets of thesepollution prevention activities in order to more broadly and rapidlyadvance the field of waste minimization.

At chemical manufacturi ng facilities, the situations sometimesencountered indicate the possible uses of chemical process wastes, in whichtwo or more waste streams, although not useful individually, may becombined to yield a worthwhile product. Such a case was examined as partof the waste reduction program at North Carolina State University. Themanufacturing facility under consideration i s engaged in the productio n ofspecialty chemicals from a primarily batch operational basis. The re aretwo primary waste streams (spent sulfuric acid and gaseous amnonia)resulting from this plant operation which, although currently disposed of,might be combined to yi eld a saleable product. Thus thi s industrialsituation emerged as a candidate for further technical evaluation. Thewaste minimization opportunit y represented a series of generic situationsin which two byproducts are necessary to develop a favorable alternative.


6/13


7/13

Th e environmenta l receiver affected by the combining and sale of thetwo byproduct stream is the atmosphere f o r the gaseous am o n l a stream.However si nce the amnonia byproduct i s presently treated in compliance withall regul ations, the environmental benefits due to an alternate use of thismaterial are minimal. In a similar manner the spent sulfuric acid ispresently used commercially on a local basis and hence no chan ge inenvironment is expected. This c ase study demonstrates the potentialincrease in value and lowering of present trea tmen t cost associated withcombining t w o byproduct waste streams, rather than any substant iveenvironmental improvement.

PRO ESS AND WASTE MINIMIZATION ASSESSMENT

The was te minimizat ion group visited a medium size chemicalmanufact uring plant during thi s project. The plant operati ons andsynthesi s unit processes were observed in detail. The first waste streamo interest is a sulfuri c acid stream of about 25% strength. Sulfuric acidis used in thi s facility in the sulfo nation and solvation o f esters, fats,oils, etc., hence this was te stream cont ains trac e amounts of organicimpurities. It is believed, however, that these impurities are not presentin sufficie nt quantity nor are these sufficiently toxic to necessitateremoval from th e acid stream, in the event that the stream is to beutilized. At present this facility i s generating about 30,000 gallons permonth of this waste acid, which is then used commercially.


8/13

P

The othe r waste strea m under conside ratlon consists of gaseousammonia, generated as a byproduct I n several dlfferent reactions.Currently, th is amnonia i s decomposed to nonh azard ous products in a hightemperature flare. By heating the ammonia to around 2,200 F, it isdecomposed to diatomic nitrogen and hydrogen. The hydrogen then burns aswell, the end result being that the ammonia is disposed of without theformation of any nitrogen oxides.

Based on our assessment of the waste streams and the application ofchemical reac tion and ther mody namic principles, it was concluded that aninnovative Bhigher value product could be achieved for thi s manuf actur ingoperation. Th e reaction o f ammonia with an aqueous solution of sulfuricacid is a si mpl e acid-base neutralization:

2NH3 + H2SO4 NH4)2SO4

the sulfuric acid and, particularly, the amnonia productionpractical way to store gaseo us amnonia) a batch production

would involveng the ammon

suitable. One simple approach to the problemwith sulfuric acid solution and introducsparger loca ted near the bottom o f the tank.

Suff icien t conta ct to enable reac tion could be achieved by bubbling t he NH3gas throu gh th e acid solution. Because of the intermittent nature of both

(there being nomode seem s mostfilling a tanka by means o f a


9/13

Pa

Because o f the rapidity of the neutralization reaction, near totalconversion could probably be achieved without the loss o f significantamounts of NH3 vapor. Since the pH of the solution would be on the acidside throug hout the course of the reaction, ammonia volatilization would beminimized. The progress of the reacti on could be tracked by monitoring thesolution pH Introduction of NH3 would be stopped when the solutionreached the desired pH. The actual value of thi s target pH will involvesome compromise, depending on t he mode and length of storage of t he productamnon ium sul fat e solution. Maint ainin g the solution at low pH would, asstated, minimize the problem of ammonia volatilization, but would tend toaccel erate corrosion, thus necessitating the use of more expensivematerials. Conversely, stora ge at high (alkaline) pH would minimizecorro sion but would lead to more noti ceabl e NH3 fuming.

It wou ld also be necessary in thi s production scheme to provi de forthe removal o f the large amount o heat generated by the neutralizationprocess, sin ce high tempe ratur es lead to accelerated corrosion. The re aretw o way s o f minimizing the heat bui dup: first, through the des ign of anexternal heat exchange system using cooling water or some oth er heattra nsf er medium. The second appro ach is to remove heat by bubbling airthrou gh the solution. Although the solut ion would be below the normalboiling point , the bubbling air would evapo rate enough water so that thelatent heat consumed would offset the heat o f neutralization. If the airbubbling metho d proves feasi ble it will clearly be much cheap er (hencepreferable) than external heat exchange.


10/13

P

This method of production could be Implemented easily by installing areactor with an air feed line and an amnonia feed line bled o f f the alreadyexisting am nonia fl are feed line.

At this stage, it appear s technically feasibl e to generate amnoniumsulfate although a number of important engineering design parameters willhave to be specified and possi bly some pilot tes ts conducted. This wouldbe th e next stage I n development of this overall scheme to better utilizewaste byproducts.

In addition, the market for ammonium sulfate fertiliz er in thevicinity of t he plant needs to be gauged with respect to whether customersexist with the capability of handling liquid ferti lizer products, and ifso, the possible selling price of the ammonium sulfa te needs to beascertained.

In the event th at the project appears worthwhile after these questionsare answered, additional f act ors will need to be dealt with, such as how todeal with the seasonal fluctu ations in the fertilizer market, how to handlebulk stora ge problems, and how to ensur e the purity of the product in viewof the many different processes from which the waste material is de r i v ed .


11/13

P

ECONOMICS

Most of the comnercial amnonium sulfate ferti izer presently producedis sold as a crystallized, dry solid. This is mainly due to the fact that,unlike some other fer tllize r products (amnonium nitrate, etc.) amnoniumsulfate is only soluable in water up to about 42% by weight. This factmakes it generall y uneconomical t o sell amnon ium sul fate in liquid form dueto t he high cos ts involved in shipping dilute solutions.

However, it has been found that there is in fact a North Caroli namarket f o r ammonium sulfate in solution form. An aqueous solution o fammoni um sulf ate (a lso a byproduct from an industrial process) is currentlybeing marke ted in fairly large quantities (10,000 tons/yr.) throug hout theeaste rn porti on of the state. This material is sold on the basis ofcontaining 7% elemental nitrogen, essentially identical to the projectedproduct o f th e proces s under study, and is not marketed extensively inweste rn North Carolina because of the geographical source of th e product,thu s making it too expen sive for shipment to thi s region. Sin ce thefacil ity unde r consi derati on is located in the western portion of thestate, the re should be a rea dy market for any a mnoniu m sulfate produced.

The re are t wo possible ways of distributing such a product. The firstis through a commercial distributor, the second, by dealing direct ly withlocal farmers. Although dealing with a distribu tor would involve much lesseffort on the part of the company, there is seri ous doubt as to wheth er it


12/13

Pa

would be prof itab le to operate in t his manner. Although the anmoniumsulfate solutlon currently available In the easte rn part of the state issold to fanners for 17/ton, the distributor only pays the producer o f thematerial about l/ton. This is due to the fact that this company generatessuch a large amount of ammonium sulfate in one location that there isdifficulty in marketing the product. With thi s oversup ply of product, theproducer s only able to charge just enough to cover expenses. While thismay be satisfa ctory to this producer, which generate s a large volume o fwast e and has no other market outlet, it would not be acceptab le to thecompany under study, which generates a much smal ler amount of waste and hasalternate met hod s of disposal. It is possible, of course, that thedistributor might be persuaded to pay a higher price f o r the ammoniumsulfate from this new source, but prospects are doubtful.

A more likely possibility for obtaining a higher selling price for them o n i u m sulfate is direct dealing with local farmers. Since the volume o ffertili zer produced would be fairly small, thi s might be a manageablealternative. Ther e may be other nonfarm mark ets as well, such as DOTright-of ways, golf courses, institutional uses, etc.

Operating in this manner would allow more o f a p r o f i t to be m de t hanworking with a distributor, however, the exact price that could be obtainedfor the material i s still unknown at this time, therefor e the economicfeasibility o f this project is still uncertain.


13/13

Pa

At this stage, the technical factors appeared feasibl e for generatingaamonium sulfate from chemical byproducts. However factor s outside thewaste minimization considerations have dictated that the amnonium sulfat ewill not be produced. A s is often the case, market conditions c hange andin this case the need for the product from which ammonia gas was abyproduct has been reduced such that furthe r production was eliminated.The industry has switched t o other products. Thus the opportunity for thiswaste minim izati on is eliminated. A s a feedback to t he overall process bywhich resources are applied to stimulate waste minimization, this casestudy describe s that which may not be uncommon. Not all concep ts deve lopedas means o f pollution prevention can be implemented since factor s outsid ethe technical aspects for such waste reduction are also very important.Thus it i s important to undertake as much screening and continualre-evaluation to assess both the technical factors and the broaderindustrial sett ing in which all process modifications or recycle/reuse mustbe placed.

processing industrial byproducts to yield as fertilizer

Documents