Equipment Cleaning

Carl Fromm

I

Session I1 Source Reduction

MINIMIZATION Of PROCESS EQUIPMENT CLEANING WASTE

Carl H. Fromm

Srinivas Budaraju

Susanne A. Cordery

Jacobs Engineering Group Inc. HTM Division 251 South Lake Avenue Pasadena, Cal i fornia 91101

ABSTRACT

The was te associated with cleaning of process equipment is probably a s ignif icant

contr ibutor t o t h e t o t a l was t e volume generated by industry. This paper addresses t h e

following a spec t s r e l a t ed to equipment cleaning was te generation:

o o Reduct ion of c leaning frequency

Review of reasons for cleaning process equipment

o

o Cos t s assoc ia ted wi th cleaning

Reduct ion of quant i ty and toxici ty of cleaning was te

Equipment cleaning techniques, media , and the i r appl icat ions are reviewed. Reduct ion

of cleaning frequency is addressed in t e rms of inhibition of fouling through proper

squipment design and operat ion, maximizat ion of equipment dedication, proper

production scheduling, and avoidance of unnecessary cleaning. When cleaning has t o

be performed, t h e quant i ty and toxicity of result ing was te can be minimized by

reducing clingage, amount of cleaning solution, choice of less toxic cleaning solution,

cleaning solution reuse, and o the r approaches. Application examples are given t o

i l lustrate e a c h approach.

INTRODUCTION

The current costs o f waste disposal and treatment, regulatory pressure, and concerns

about legal l iab i l i t ies have been forcing IJ.S. industries t o scrut in ize their hazardous

waste generation pract ices L/. A pr imary objective of these e f f o r t s has been t o

min imize waste generation, i.e. t o reduce the quant i ty and t o x i c i t y o f the waste.

O f the many industr ia l waste-generating operations, process equipment cleaning (PEC)

i s nearly universal in i t s appl icat ion, as i t is pract iced in all segments of manu-

factur ing industry. PEC is o f par t icu lar importance f o r discrete processes such as

batch reactions, compounding, surface coat ing operations, etc. This is because the

cleaning frequency f o r discrete processes i s generally much higher than f o r continuous

processes. However, this does no t mean tha t cleanup wastes f r o m continuous

processes can be ignored. Disposal of sludges f r o m cleaning o f heat exchanger foul ing

deposits, fo r example, i s o f t e n o f concern t o the operators o f pet ro leum refining,

petrochemical and chemical process faci l i t ies.

The in ten t o f th is paper i s t o rev iew basic waste min imizat ion strategies appl icable t o

cleaning operations. The in ten t i s to provide a s t ructured classi f icat ion of such

strategies presented in the f o r m o f a prototype checkl ist which can be used t o help

focus and plan a concerted a t tack on waste.

WHY EQUIPMENT IS CLEANED

Equipment cleaning i s a maintenance funct ion typ ica l ly per fo rmed for the fo l lowing

r e as0 ns:

- t o restore or main ta in the operat ing ef f ic iency o f equipment, e.g., t o

restore adequate heat t ransfer ra te and low pressure drop in heat

exchangers. - t o avoid or l imit product contamination, e.g., when a paint m i x tank needs

t o be cleaned between batches of varying paint formulations.

t o min imize corrosion and extend equipment l i fe t ime.

t o al low for inspect ion and repai r o f equipment.

t o improve appearance (exter ior surfaces only).

- - -

The need f o r cleaning is a d i rec t consequence of deposits fo rmed on t h e sur faces

exposed t o t h e process environment. Some of t h e major routes and origins of deposit

format ion are summarized in Table 1 along with descriptions and s o m e examples.

Understanding how and why t h e deposits a r e formed is a c r i t i ca l first s t e p in any waste minimization e f for t . I t is an especially important a spec t for equipment and

process designers, because t h e need for equipment cleaning can o f t en be reduced or e l iminated through design modifications a t minimal expense during the design s tage .

A common sense approach t o minimizing was te f rom equipment cleaning opera t ions is

to pose and answer the following sequence of questions:

- - how can cleaning be curtai led or avoided (i.e., c leaning frequency

why is t h e deposit present?

reduced)?

- when cleaning is necessary, which cleaning method and medium will

g e n e r a t e t h e leas t amount of l ea s t tox ic waste?

Sect ions below address major a spec t s re la ted t o t h e l a s t two questions.

REDUCTION OF CLEANING FREQtlENCY

Generally, t h e need fo r cleaning can be reduced or avoided a l toge the r by t h e

application of t h e following measures:

- - maximizing dedicat ion of process equipment t o a single formulat ion or

inhibition of fouling or deposi t format ion rate .

function.

- proper production campaign scheduling.

- avoidance of unnecessary cleaning.

Inhibition - of fouling is of par t icu lar impor tance in hea t t r ans fe r appl icat ions where it

can be accomplished through a variety of means, including use of smooth h e a t t ransfer

sur faces , lower fi lm tempera tures , increased turbulence, control of fouling precursors

and proper choice of exchanger type.

TABLE 1. TYPICAL ROUTES AND ORIGINS OF DEPOSIT

FORMATION IN PROCESS EQUIPMENT

Route/Origin Description

Crystal l izat ion

Sedimentat ion

Major problem in evaporators and crystal izers (e.g. very f r equen t in food processing).

Major problem in petroleum ref inery crude unit desal ters and oil s t o r a g e tanks. Also present in cooling tower basins.

Chemical react ions and polymerization Buildup on the internal r e a c t o r sur- faces are of ten encountered (e.g. allyl chloride synthesis). Also of importance in c rude oil s to rage tanks.

High t e m p e r a t u r e coking

Corrosion

Bacter ia l growth (biofouling)

Clingage (of importance to solvent

. cleaning applications)

Carbonaceous mater ia l depositing on walls of furance tubes (e.g. fu rnace fo r ethylene chloride pyrolysis).

Common problem in h e a t exchangers in chemicals and allied products industry.

Major problem on cooling-water-side of h e a t exchangers in e l ec t r i c power production.

Residual c o a t of process liquid l e f t after drainage; major problem in r e a c t o r s and mixers in t h e paint manufactur ing industry and generally in all high-viscosity liquid t r ans fe r operations.

The use of smooth h e a t exchanger surfaces results in lowering the adhesion of the

deposit or its precursor t o the surface. Application of electropolished s ta inless s t e e l

tubes in a fo rced circulation evaporator used in black liquor service in a paper mill

resulted in a d rama t i c reduction of cleaning frequency f rom once a week t o once a

year 2/. Smooth non-stick surfaces can also be provided by Teflon (a regis tered t r ademark of E.I. Dupont de Nemours Sr Co.). Teflon heat exchanger designs a r e

commercially available, as are designs utilizing Teflon coated steel . In a s e p a r a t e

application, condensers using Teflon-coated tubes have been shown t o drastically

reduce fouling and resis t corrosion while maintaining high thermal efficiency. The

higher cost of ma te r i a l was weighed against reduced energy cost t o show a 69 pe rcen t

r e tu rn on investment in the first year before tax =/. If reduced cleaning costs were

to be added, t h e ROI would have been higher.

The rate of h e a t exchanger fouling in a given service is dependent upon fluid velocity

and, qui te of ten, on fi lm temperature . Film t empera tu re controls t h e speed of

chemical react ions which resul t in deposi t-forming compounds while fluid velocity

controls t h e shea r r a t e at t h e fluid-deposi t interface.

Hence, lowering t h e t e m p e r a t u r e of the heat ing medium and increasing t h e fluid

velocity (e.g. by recirculation) can produce a desired reduction of t h e fouling rate. An

economic trade-off analysis between the inc rease in pumping c o s t and t h e dec rease in

t h e cost of cleaning and o the r possible savings appears warranted in investigations

relating t h e deg ree of oversizing t o cleaning w a s t e generation. A general review of

t he rma l and hydrodynamic aspects of h e a t exchanger fouling w a s provided by

Knudsen 21.

Control of deposit precursors is .often an obvious practical consideration. Proper

ma in tenance of cooling w a t e r quali ty in open circulating sys t ems is of paramount

importance to water-side hea t exchanger fouling. Control of hardness, pH, corrosivity

and biofouling tendency is accomplished through careful monitoring of w a t e r

quality E/ . In par t icular , biocides added in treatment must propagate t h e e n t i r e

cooling fluid pa th in order t o be deposited and function a t all locations in t h e

exchanger; and acid f eed equipment t o maintain the pH in the non-scaling range of

6 to 7 mus t be rel iable or else rapid scaling or corrosion problems occur I / .

The choice of h e a t exchanger type can influence cleaning frequency. For example,

spiral p l a t e exchangers a r e o f t en specified over o the r designs in fermentat ion plants,

owing to the e a s e of solid resuspension, absence of pockets, and non-plugging

character is t ics . Rod baff le design provides more effective shell-side turbulence a t lower pressure drop compared to a more conventional segmented baf f le design.

Therefore , t h e rod baff le design can be expec ted to exhibit superior shell-side fouling

charac te r i s t ics .

Slowing down the r a t e of deposit formation is not l imited t o hea t exchangers, bu t a lso

is impor tan t for o the r types of equipment. For example, crude oil's exposure t o

a tmospheric oxygen can cause formation of gums and resins during long exposure

periods inside s to rage tanks. The use of floating roof tanks o r iner t gas blanketing has

been suggested as a way t o reduce t ank deposi t buildup si. Similarly, in paint

manufactur ing, exposure t o air causes formation of solid fi lms t h a t adhere strongly to

the internal sur face of t he mixers. This can be avoided by using closed s to rage and

t ransfer systems, as evidenced by experience a t Ford Motor Company. A t Ford, t h e

paint s to rage and t ransfer sys tem was enclosed and redesigned f o r full recirculat ion

result ing in less f requent and eas ie r cleanups and an improvement of paint quali ty 21. Other applications of fouling inhibition include coat ing of reac tor in te rna ls with

special chemica ls t o prevent sca le formation. These prac t ices have been used in t h e

suspension polymerizat ion process for polyvinyl chloride 61.

Maximizing dedicat ion - of process equipment t o a single process func t ion or formulat ion will reduce cleaning frequency, as t h e frequency of switching t o d i f f e ren t

formulat ions will diminish. Maximum dedication means e i ther converting f rom a ba tch

to a continuous process or using t h e equipment in te rmi t ten t ly just for one formulation.

Historically, t h e changeover f rom ba tch or cyc l ic t o continuous operat ions has been . common in t h e chemica l industry, .owing t o increased product demand, increased labor

costs and technological progress. The advantages of t h e continuous process over ba t ch

include t h e ease of automat ion and control (which minimizes human e r ro r leading t o

inferior product quali ty) and lower labor requirements .

The choice be tween t h e continuous or ba tch mode is governed primarily by production volume and r e l a t ed t rade-offs between capital and operat ing costs. The ba tch process

is advantageous in s i tua t ions where production volumes are small and product diversity

large. Batch processes have proven advantageous even for cer ta in la rge volume

1

products, such as, neoprene

- -7- .’ were developed but fa i led t o

rubber and phenolic resins, where continuous a l t e rna t ives

find wide application %/.

Dedicating a piece of equipment t o a single formulation in t h e batch process means

t h a t the equiprnent remains dormant between individual production campaigns.

Cleaning a f t e r each campaign can be avoided provided t h a t ma te r i a l s l e f t in t he

equipment do not d e t e r i o r a t e with t ime or corrode t h e internals. Also, t h e cos t

penalt ies associated with equipment under-utilization must be outweighed by cleaning

cos t s incurred when t h e equipment is used with m o r e than o n e formulation.

Proper production scheduling is a commonly invoked method t o dec rease cleaning

frequency. Equipment uti l ization s t r a t eg ie s and t h e resulting production schedules

should be derived through optimization analysis, where t h e object ive is t o meet t h e

desired production goals with due consideration of such constraints as available

equipment, c o s t of turnaround, labor availability, s torage, etc. Meet ing production

goals is t o be accomplished with minimum cost , which includes minimization of cleaning frequency. A gene ra l review of optimum s t r a t egy formulation w a s given by

P e t e r s and T immerhaus ?,/.

However, in a typical s i tuat ion a formal optimization analysis is not used of ten.

Ra the r , a common-sense approach t o production scheduling is used based o n trial-and-

error preparat ion of production bar-charts. To reduce cleaning waste , it is generally

desirable t o schedule long campaign runs, as opposed t o short and more f r equen t runs.

Production schedulers now mus t be aware of t he current was te disposal costs , a n

a spec t t h a t previously could have been ignored.

Avoidance - of unnecessary cleaninq should be one of the goals of was te minimization

audits. A t times, equipment cleaning is performed routinely with l i t t l e or no

consideration of the r a t iona le for the cleaning activity. An ac tua l case is known

where a ball mill was used periodically t o wet-grind a cer ta in powder. The ball mill

with corrosion-proof in t e rna l s was total ly dedicated t o t h e s a m e formulation, a s t a b l e

mixture of inorsanic powders. Ye t , t h e ball mill was cleaned after e a c h use for no

apparent reason, IJpon questioning, t h e only justif ication provided was t h a t t h e o the r

non-dedicated ball mills a t t h e facil i ty were cleaned a f t e r eve ry use.

REDUCTION ff QUANTITY AND TOXICITY OF CLEANUP WASTE

When cleaning has to be performed, it should be performed e f f ec t ive ly with minimal

generation of waste. Typical considerations include t h e choice of cleaning medium, cleaning technique and w a s t e disposal option. A brief overview o f t hese choices (with

the exception o f waste disposal), is provided in the following paragraphs.

A distinction can be m a d e between chemical and mechanical cleaning, Chemical

cleaning requires the use of substances such as those shown in Table 2 which are

employed t o chemically attack t h e deposits and render t h e m e i the r solvent or wa te r -

soluble. The basic r eac t ion types include oxidation, reduction, chelat ion or conversion

of insoluble oxides into soluble salts. Cleaning formulations also include su r fac t an t s t o

lower su r face tension of solution t o allow for f a s t e r penetrat ion and breakup of

deposits.

Physical or mechanical c leaning relies on breaking t h e adhesion of t h e deposit t o a surface using mechanical devices, such as scrapers, squeegees, rags, drag lines, "pigs", lances or through the use of high velocity wa te r jets (hydroblasting). Of t en

mechanical and chemical cleaning are combined, e.g., when high velocity jets are employed with caustic solutions t o attack deposits in paint mix tanks.

According t o a classification developed by Loucks E/, six sepa ra t e cleaning

techniques are distinguished:

- fill-and-empty technique

- circulat ion technique - "flow over" technique .

- gas propel technique

- process s imulat ion technique

- onstream cleaning technique

In the "fill-and-empty" technique, a process vessel is isolated from o the r equipment

and filled with an appropr i a t e cleaning solution. The solution can be hea ted and

ag i t a t ed and, a f t e r a period of 4 t o 8 hours it is drained. Rinse-water or diluted alkali

or acid solutions are then used t o remove residual cleaning chemical. Drained

chemicals and subsequent rinses are either reused, t r ea t ed , recycled or land-f illed

TABLE 2. SOME CHEMICAL CLEANING COMPOUNDS AND THEIR USAGE

Cleaning Compound Chemical Ac t ion Usage Remarks

Corrosive t o steel; tempera- tures must be below 175OF

Hydrochlor ic A c i d

Sul fur ic A c i d

N i t r i c Ac id

Hydrof luor ic A c i d

Sulfamic Acid

C i t r i c Ac id

Dissolves most water scales and corrosion products

Dissolves most corrosion products

Same as HCI

Used on boilers, heat exchangers, p i pe l i nes, e tc.

L i m i t e d use Cannot remove water scales

Used f o r stainless steel and aluminum

Cannot be used f o r copper and ferrous alloys

Dissolves s i l icate deposits Used as an addit ive t o HCI (as ammonium bif luoride)

Very dangerous t o handle

Dissolves ca lc ium salts Used as an addit ive t o HCI Easy t o handle; soluble ca lc ium salts

Dissolves i ron oxides Used most ly t o clean boilers; f requent ly w i t h added ammonia and oxidizers

N o t good for water scale removal

Caust ic Soda, Soda Ash Dissolves o i l and grease Used t o remove o i l and grease before ac id cleaning and t o neutra l ize the acid a f t e r cleaning

Dangerous t o handle

A rnmoni a Forms soluble complexes w i t h copper ions

Used t o remove copper f r o m large boi lers

Needs t o be handled carefu l ly

Ethylene Diamine Tetra-Acetate (:EDTA)

Dissolves water scales a t alkal ine pH's

Used f o r cleaning water systems Expensive w i thout shutdown

Source: References (lo), (20).

depending on the i r composition and the availability of disposal options at t he

particular site. The method uses large quantit ies of chemicals and requires substant ia l

downtime. It is typically applicable t o small vessels, tanks or hea t exchangers.

In t h e "circulation" technique, t he vessel is filled with cleaning solution t o an overflow

and allowed to s tand for a sho r t t ime period, a f t e r which the solution is c i r cu la t ed

with an auxiliary pump. Fresh make-up solution can be pumped in i f used solution is

dithdrawn. In boilers, nitrogen gas is used t o provide agitation f o r more effective

sca l e removal.

The "flow over" technique consists of spraying the solution onto the surface. I t is

applicable t o large tanks where cleaning by filling or recirculation would require

excessive quanti ties of cleaning solution. Extra safety precautions are usually

necessary.

The "gas propel" technique uti l izes cleaning agents t h a t are not overly corrosive at higher t empera tu res when s t e a m is used t o propel t hem through t h e system. This technique is usefu l for pipelines, where inhibited organic acids or che lan t s a r e

entrained into a flow of steam which ca r r i e s t he liquid drops and solids debris through

hydraulic obstacles of t h e system.

The llprocess simulation" technique is applied t o equipment t h a t is easily fouled and

where spare parallel units a r e provided. Fouled equipment is' cleaned by s imulated

process operation, where t h e equipment is isolated, drained o f process fluid and fi l led

with t h e cleaning solution using process pumps and controls t o maintain flow and

temperature . An example is removal of iron oxide and copper deposits f r o m high

pressure steam.generat0r.s using ammoniated EDTA solution.

The "onstream cleaning" technique is probably t h e mos t preferable method, as i t re l ies

on process fluid t o do t h e cleaning during normal operation. Of t en auxiliary mechanical devices are used along with additives, such as EDTA or acids to p romote

deposit removal. This technique is used fo r cleaning r eac to r jackets, gas compression s ta t ion engines, h e a t exchangers , and o the r equipment. In-service cleaning of large

circulating cooling w a t e r systems is of ten done through in t e rmi t t en t pH swing t o t h e

acid side of neutral and back again. Among many mechanical devices used in conjunction with ons t r eam cleaning, one could mention r am valves for rodding ou t

plugged nozzles and moveable hea t exchanger tube inserts propelled by reversing

process fluid 111. In a s e p a r a t e example, the use of fluidized beds of ine r t solids (e.g.,

sand) was found useful in h e a t t r ans fe r applications cha rac t e r i zed by e x t r e m e fouling,

such as heat recovery from geothermal brines. Solid particles constant ly ab rade t h e

deposit away from the hea t t r ans fe r surface, maintaining high t r ans fe r ra tes .

The choice of cleaning method and media, a p a r t f rom cost , should also be based on t h e

following environmental considerations:

- minimize t h e amoun t of cleaning solution used; - -

choose t h e medium ul t imately result ing in t h e l e a s t toxic waste;

determine ahead of t i m e how the cleaning w a s t e is going t o be disposed of.

The use of chemical cleaning (e.g., with mineral or organic acids) resul ts in

appreciable quant i t ies of hazardous cleaning wastes which need t o be t r e a t e d prior t o

disposal. As appropriate t r e a t m e n t faci l i t ies a r e not available ons i t e in eve ry case, mechanical cleaning and ons t r eam cleaning appear preferable t o chemica l cleaning.

According t o information obtained from various cleaning contractors , t h e s e f a c t o r s are gaining recognition as t h e r e c e n t t r e n d has been more toward hydroblasting and

ons t r eam cleaning and away f r o m chemical cleaning. This was a t t r i bu ted t o t h e rising

cos t s of was te disposal and t r e a t m e n t .

When chemical cleaning is unavoidable, t he l e a s t toxic medium should be chosen; for

example, an alkaline c l eane r would be preferable over a halogenated solvent. How-

ever , if the toxici ty of the "soil" t o be removed is the controlling f a c t o r , t h e cleaning

a g e n t with a higher potent ia l fo r recovery and reuse should be used.

An attractive a l t e rna t ive t o those cleaning methods t h a t require disassembly of

equipment fo r cleaning, is a clean-in-place (CIP) system. The s y s t e m is composed of

tanks, h e a t exchangers, f i l ters , pumps, piping and instrumentat ion permanent ly

installed as an auxiliary sys t em designed to circulate a controlled inventory of

cleaning solution through isolated process equipment of ten using spray manifolds or

-*-I--- Iiniiirl j e t nezz!es inside p r e d g c t i o ~ vessels. The C!p systems gener&y reduce t h e

usage of cleaning medium. They are especially e f f ec t ive when coupled wi th high

velocity au tomated jet manifolds and s t aged counter-current rinsing; an 80 t o 90

pe rcen t reduction in aqueous was te was achieved by paint manufac tu re r s a f t e r

installing high pressure spray nozzles fo r tank rinsing g/. CIP systems a r e popular in

food, pharmaceut ical and paint industries; however they a r e uti l ized less frequent ly in

t h e chemical processing industry u/. Reuse of cleaning solutions is common in CIP systems. In general , r euse of cleaning

solutions is highly desirable, especially i f they can be utilized as p a r t of formulation.

For example, a considerable reduction in r eac to r cleanup w a s t e was achieved by

Borden Chemical where a two-step rinse sequence was applied t o a batch k e t t l e

arrangement used for phenolic resin synthesis. The f i r s t rinse used a small amount of

w a t e r generat ing a concen t r a t ed s t r e a m which could be recycled t o t h e process. The second full volume rinse generated was tewa te r with a much lower c o n t e n t of toxic

ma te r i a l t han a previously used single rinse method 141. Other examples include reuse

of rinsewater f rom l a t ex tank cleaning as pa r t of la tex formulat ion in t h e paint

industry 151 and use of w a r m oil f o r flushing t h e deposits ou t f r o m c rude oil s t o r a g e

tanks in a n oil refinery, followed by solids separat ion in the slop oil sys t em !&/.

The preceding sect ions were concerned with reduction of cleaning frequency and with

the choice of t h e l ea s t waste-intensive cleaning methodology. There is a r e l a t ed , b u t

independent a spec t of cleaning w a s t e reduction, i.e., reduction of clingage. As

explained previously, clingage is the amount of process ma te r i a l l e f t inside t h e vessel

or o the r equipment a f t e r draining. In operations involving viscous fluids, such as paint

manufactur ing and resin compounding, clingage is an important consideration as i t not

only resul ts in was te which is expensive t o dispose of, but also r ep resen t s a d i r ec t loss

o f product or raw mater ia l .

To reduce clingage, t h e following measures should be considered:

- - - - - choice of square cylindrical or spherical geometry t o minimize w e t t e d

provision of adequa te drainage t ime;

use of low-adherence surf aces, e.g., fluorocarbon or electropolished steel;

use of mechanical wall wipers (dual s h a f t mixers);

use o f manual wipers or squeegees;

surface;

rotat ion o f ag i t a to r a f t e r batch dumping t o reduce clingage on t h e blade. -

All of the above measures are self-explanatory and do not require elaboration. $Most a r e prac t iced extensively throughout industry. The use of t ank linings a s a means o f

reducing adherence and preventing corrosion has been addressed by Zolin g/ and

Kays !&!I, The use of dual sha f t mixers with slow scraper blades wiping t h e walls and the bot tom of mixing tanks is common in applications involving viscous liquids E/,

COST OF CLEANING

The cos t of cleaning c a n be viewed as being composed of the following elements:

D i rec t C o s t s

- equipment assembly/disassembly

- cleaning chemica ls and supplies

- was te t r e a t m e n t and disposal

- cleaning labor and supervision

- cleaning equipment depreciat ion

- uti l i ty cos t s

Ind i rec t Costs - planning and scheduling

- cost of los t production - - inspection and tes t ing

- process equipment deter iorat ion

cos t of los t raw mater ia l s inventory

Of t en equipment cleaning is performed by outs ide cont rac tors with specialized

equipment who assume t h e responsibility for hauling away t h e w a s t e and for disposing

of i t properly.

Costs of c leaning vary widely depending upon t h e medium, method and application.

R e c e n t inquiries into t h e cost of cleaning of h e a t exchangers es tabl ished t h e following

compilat ion of re la t ive h e a t exchanger cleaning cos t s using con t r ac t ed service:

Method Relat ive C o s t Hydroblas t ing 1.0

Rodding 4 t o 5 Chemical Clean ing:

Without was te disposal 0.3 t o 3

2.1 t o 4 W i t h was t e disposal

In many cases t h e cost of cleaning ( taken as d i rec t cost only) is lumped toge ther with

o the r main tenance costs. As a resul t , p lant management may no t have good visibility

of t h e ac tua l cos ts of cleaning, which may impede management 's support fo r was te

minimization effor ts . Often, when plant management learns of t he true cos t

dimension, ac t ion t o lower cleaning cos ts is quickly init iated.

SUMMARY

As mentioned in t h e introduction, t h e in ten t of this paper is to provide a brief review

of techniques, approaches and s t r a t eg ie s for minimizing equipment cleaning was te and

to provide a classification scheme tha t may serve as an init ial guide t o those

in te res ted in was te minimization. Such a classification or summary is provided in

Table 3. This se rves a s a prototype checkl is t f o r addressing all waste minimization

issues in a logical sequence.

The subject of equipment cleaning is qui te diverse a s the funct ion is performed in

virtually eve ry industry. General izat ions presented in this paper must be t rans la ted

into si te-specif ic and exac t ing requi rements in any was te minimization effor t .

ACKNOWLEDGEMENTS

The authors wish t o express the i r g ra t i tude t o the U.S. Environmental Pro tec t ion

Agency, Of f i ce of Solid Waste, fo r the i r support in developing a substant ia l portion of

the ma te r i a l p resented in th i s paper.

,

TABLE 3. WASTE MINIMIZATION OF EQUJPMENT

CLEANING WASTE - SUMMARY OF APPROACHES

REDUCE CLEANING FREQUENCY

1. Inhibition of fouling r a t e - smooth hea t t r ans fe r sur faces

- lower film temperature/higher turbulence

- control of fouling precursors - choice of h e a t exchanger type

2. Maximize process equipment dedication - - dedication t o single composition

conversion f rom ba tch to continuous operat ion

3. Proper production scheduling

4. Avoidance o f unnecessary cleaning

I

REDUCE QUANTITY AND TOXICITY OF WASTE

1. Minimize amount of cleaning solution

- high pressure nozzles

- flow-over technique

- on-stream cleaning - use of CIP systems with s taged or counter-current

rinsing

- reuse of cleaning solution

Minimize toxici ty of spent cleaning solutions

- clingage reduction -

2.

mechanical (hydroblasting) over chemica l cleaning

REFERENCES

1.

2.

3.

4.

5 .

6 .

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

League o f Women Voters of Massachusetts, Waste Reduction: The U n t o l d Story, Conference held June 19-21, 1985 a t Nat ional Academy of Sciences Conference Center, Woods Hole, Massachusetts.

Uddeholi n Corporat ion (Sweden), Technical brochure on Tubec Tubes and communications w i t h Avesta Stainless Inc., Totowa, New Jersey

Knudsen, J.G., Foul ing o f Heat Exchangers: Are W e Solving the Problem?, Chem. Eng. Progress, Feb. 1984, pp. 63-69.

Jacobs Engineering Group Inc., Al ternat ives for Hazardous Waste Manaqement Pract ices in the Petro leum Ref in ing Industry, EPA-530-SW-l72C, Washington, D.C., U.S. Environmental Protect ion Agency, 1979.

Colleta, V., Powers, J., Chem Proc. 44(4):20-1, 1981.

Cameron, J.B., Lundeen, A.J., McCulley, Jr. J.H., Hydroc. Proc., 59(3):39-50, 1980.

Euleco S.P.A., Euleco Continuous Process: Technical Bul let in, 1975.

Shell Internat ional Research Inc., Brit. Patent No. 136, 189; issued Dec. 11, 1968.

Peters, M.E., Timmerhaus, K.D., Plant Desiqn & Economics f o r Chemical Enqineers, 3rd Edit ion, McGraw Hill Book Co., 1980.

Loucks, C.M., Boostinq Capacit ies w i t h Chemicals, Chem. Eng. (deskbook issue), 80(5):79-84, 1973.

Water Services o f America, Inc., Superscrubber Technical Bul let in, 1985.

U.S. Environmental Pro tec t ion Agency, O f f ice of Water & Waste Management; Development Document for Proposed Ef f luen t Guidelines, N e w Source Per- formance Standards and Pre t rea tment Standards for the Pa in t Formulat inq, Pa in t Source Category, EPA-440-1-79-0496, Washington, D.C., 1979.

Hyde, J.M., New Development in CIP Practices, Chem. Eng. Progress 81(1):39-41, 1985.

6

Huisingh, D., et. al., Proven P r o f i t f rorn Pol lu t ion Prevention, The I n s t i t u t e f o r L o c a l Self-Reliance, Washington, D.C., 1985.

Ri ley, J.E., Development Document fo r E f f luen t L i m i t a t i o n Guidelines, New Source Performance Standards f o r t h e T i re and Synthetic Segment of t h e Rubber Processinq Industry, P o i n t Source _ _ Cateqory, EPA-440-1-74-013A, U.S. Environ- menta l Pro tec t ion Agency, 1974.

Barnett, J.W., Bet ter *Nays t o Clean Crude Storage Tanks and Desalters, Hydroc. Proc. 60(1):82-86, 1980.

Zolin, B.I., Chem. Proc. 47(9):63-5, 1984.

REFERENCES (Continued)

18.

19.

20.

21.

Kays, 'N.B., Construct ion o f Lininq f o r Reservoirs, Tanks & Pollution Control Facil i t ies, Wiley, New York, 1979.

Myers Mixing Company: pr ivate communication, 1985.

Betz Laborator ies Inc., Handbook o f Industrial Water Conditioning, 8 t h Ed., Trevose, Pennsylvania 1980.

Paschke, L.F., Condensing Hea t Exchangers Save Heat , Chem. Eng. Progress , pp. 70-74, July 1984.

MINIMIZATION OF PROCESS EQUIPMENT CLEANING WASTE

CARL H. FROMM

JACOBS ENGINEERING GROUP INCORPORATED PASADENA, CALIFORNIA

Presented at the U.S. EPA SYMPOSIUM ON

SOLVENT WASTE REDUCTION ALTERNATIVES

CONTENTS

1.

2.

3.

4.

5.

6.

7.

Why Equipment is Cleaned?

Conceptual Approaches to Waste Minimization

Why Deposits Form?

Reduction of Cleaning Frequency

Reduction of Quantity and Toxic of Cleanup Waste

Cost of Cleaning

Summary

I . WHY EQUIPMENT IS C LEANED?

To Restore/Maintain Operating Efficiency

To Avoid or Limit Batch Contamination

To Reduce Corrosion and Extend Equipment Lifetime

To Allow for Inspection/Repair of Equipment

To Improve Appearance

Reaso ns for Interest in Reduct ion of Process EauiDment Cleanina (PEC) Waste

a) PEC - A Widespread Industrial Practice.

b) PEC Waste - Probably Represents a Significant Frac- tion of All Hazardous Waste Generated.

c) Economics (High Cost of Treatment and Disposal)

d) Land Disposal Ban

e) Liability Issues

f) Regulatory Incentives

g) Future Regulation

3.0 WHY DEPOSITS FORM?

Rou te/O r isi_ll

Crystallization

Sedimentation

Chemical Reactions and Polymerization

Corrosion Bacterial Growth (Biofouling)

Clingage

CONCEPTUAL APPROACH TO WASTE MINIMIZATION

HIERARCHY

Hiah 1 Environmental Desirability Low

First I Order of Exploration Low I

Minimization of PEC Waste

Order 1.

Exploration 2. of

Why Deposit is Present?

How Can Cleaning Frequency Be Reduced?

Which Cleaning Method/Medium Will Produce Least Amount of Least Toxic Waste?

How to TreaVDispose of Residuals in an Environmentally Safe and Cost Effective Way?

4.0 REDUCTION OF CLEANING FREQUENCY

Inhibition/Avoidance of Deposit Formation

Maximizing Equipment Dedication to a Single Formulation or Function

Proper Production Campaign Scheduling

Avoidance of Unnecessary Cleaning

/nhibitition/A voidance of Deposit Information

Foulina Prevention in Heat Exchangers

Use Non-Stick Tube Surfaces Control of Deposit Precursors Choice of Heat Exchanger Type

Foulina Prevention in Other ApDlications

lnhibitition/A voidance of Deloosit Information

Fouling Prevention in Heat Exchangers

ApDroach: Use Non-Stick Tube Surfaces

Appearance of a. standard tube and a Tubec rube, respec- tively, after use in a black liquor evaporator.

. .

Electropolished Tubes fcourtesv of Avesta Stainless Co.)

FOULING PREVENTION IN HEAT EXCHANGERS

Approach 2: Low Film Temperatures and Higher Turbulence.

Increasing / Surface Temperature

-

Velocity V

Source: Garret-Price, et.al.; "Fouling of Heat Exchangers", Noyes Publications, 1985.

FOULING PREVENTION IN UEAT EXCUANGERS

Awroach 3: Control of Deposit Precursors = e.g. pH and Biocide Concentration in Cooling Water

Approach 4: Choice of Heat Exchanger Type

Spiral Plate Exchanger Schematic

1NHlBITlON OF DEPOSIT FORMA TION - NOT ONL Y LIMITED TO HEAT EXCHANGERS

ExamDles

Problem

Formation of Gums and Resins In Crude Oil Storage Tanks.

Drying of Paints in Mixing Tanks and Application Equipment.

Tar Formation in Allyl Chloride Synthesis Reactor.

Solution

Limit 0, Exposure by Floating Roofs or Nitrogen Blanketing.

Enclosed Recirculation System.

Re-Design lnternals to Increase Turbulence.

One Tank - Two Products MAXIMIZING EQUIPMENT DEDICATION TO A SINGLE FORMULATION OR FUNCTION

-b

Two Products - Each With a Dedicated Tank

- *_m_

W Time A A

---

6 B

0 Avoldance of Unnecessary Cleanlng

4.0 OF F R F Q E K U

0 lnhlbltlon of Deposlt Formatlon Rate

Maxlmldng Equlpment Dedlcatlon to a Slngle . Formulatlon or Functlon

I* PROPER PRODUCTION CAMPAIGN SCHEDULING

0 Avoldance of Unecessary Cleanlng

Enhance the Use of Formal Methods for Derivation of Optimum Schedules.

Increase the Size and Duration of Campaigns.

Schedule Production Campaigns so as to Utilize Batch Compatibility to its Fullest.

Example: Light-to-Dark Batch Sequencing in Paint Manufacture

4.0 OF-

* lnhlbltlon of Deposlt Formatlon Rate

Maxlmlzlng Equipment Dedlcatlon to a Single Formulatlon or function

. Proper Productlon Campaign Scheduling

AVOIDANCE OF UNECESSARY CLEANING

Dedicated Equipment Need Not to be Cleaned After Each Use.

Cross Contamination Between Batches of Different Products May Not Be Serious Enough to Warrant an Intermediate Cleaning Step.

5.0 REDUCTION OF QUANTITY AND TOXICITY - OF CLEANUP WASTE WHEN CLEANING IS - UNAVOIDABLE

Proper Choice of Cleaning Method & Medium

Reduction of Clingage

Reuse of Cleaning Solution

w

5 c 9) S: 0

0

'D 111 0 'D m 3 0

0 m 0 n 0 r m D

0 e e e e

v) 0 - ni m I).

3 (13

cii cta 5 I.

=13 0 9. a I.

(P U c 0 3 (P

.I.

v) 0 - r-

3 v)

rc

0 E E' 5'

X

ca v) 0

0 0 3 v c X

b c) .. I m

P, v)

b

I

CHOICE OF CLEANING METHOD

Environmental Desirability a Mechanical

Chemical

On-Stream Clean-In-Place Off-Stream

On-Stream Cleaning Amertap Sponge Ball Cleaning System

c Fluidized Bed Exchangers pHSwings Ramvalves Dual Shaft Mixers

0 "Pigging" of Pipelines

REDUCTION OF CLINGAGE

Clingage - Liquid Film Residual Following Vessel Drainage. Serious Consideration in Vis- cous Liquids Processing.

Use of Low Adherence Surfaces

Use of Mechanical Wall Wipers, Manual Wipers or Squeeges

Choice of Square Cylinrical or Spherical Geometry to Minimize Wetted Surface

Provision of Adequate Drainage Time

Can Be Reduced By: - -

-

-

RESIDUAL FILM THICKNESS DURING DRAINAGE

---Am-- Initial Liauid Level

6 = (2,t)

\ Liy id ------------- Level at Time t Moving Downward with Velocity s

Reuse of Cleanina Solutions

Re-Use of Spent Cleaning Solution in Next Compatible Batch

Multistage/Counter-Current Rinsing

Recovery

CLEAN4N-PLACE SYSTEM WITH SOL VENT RECOVERY

* I Mixer .m J I

\

4 Product J

1 Spent Solvent I 0 7

Other Users

Swam Still 1111) u L

C

a- a0 cn

E .2 LJ

7.0 SUMMARY

UNDERSTAN D REASOB EQIumNw

InhibWAvoid Deposit Formation Maximize Equipment Dedication Properly Schedule Production Campaigns Avoid Unnecessary Cleaning

REDUCE QU ANTlTY/TOX CITY OF CLEANING WASTE

Properly Choose Cleaning MethodMedium Reduce Clingage Reuse Cleaning Solution

6.0 e

0

e

COST OF CLEANING Direct Costs

- Equipment Assembly/Disassembly - Cleaning Chemicals and Supplies - Waste Treatment and Disposal - Cleaning Equipment Depreciation - Utility Costs

Indirect Costs

- Planning and Scheduling - Cost of Lost Production - - Inspection and Testing - Equipment Deterioration

Cost of Lost Raw Material Inventory

Cleaning Usually Lumped Together With Other Maintenance Costs

- .. _.~. .

GEPA

Unlted Stated Center for Envlronmental offlce cf Solld Waste Environmental Protectlon Research informatkn and Emergency Response A g e w __- Technology Transfer March 1988 CERI-88-06

Solvent Waste Reduction Alternatives Seminar

Speaker Papers

'