Desafimtion,35(1980)375-382 0 Ekmier Scientific tiblishing Company, Amsterdam - Printed in The Net.herla&s

MEMl3RANE TECHNOLOGY AND COSTS; STATE OF THE ART

6. BJERKE Department of Business Administration, Lund University, Sweden.

Abstract:

It is impossible to make calculations, which are generally valid. There are too many assumptions which must be established before an individual case can be calculated, e.g. concerning volume treated, operating period and membrane 1 ife. However, one can think of an 'average' situation looked at from such a systems level that five components can be distinguished, i.e. 1) Pretreatment 2) RO Membranes 3) Post-treatment 4! Support systems 5) Acceptance test. From this point of view one can easily find crucial factors such as membrane, oper- ating/cleaning labour and depreciation costs.

Different results are reported in the literature. It looks like some indus- tries are more suitable than others from an economic point of view, e.g. brood- pulp, dairy and foodstuff.

Generally there are ques tions which are seldom as ked. Such are the role of opportunity costs, 5 tart-up problems and costs from help of experts.

There are several advantages from using membrane technology for concentra- tion, e.g. less need of energy, smaller Installations and environmental advan- tages _ These factors wi 11 be stressed even more in the future. Membrane tech- notogy has therefore come to stay.

1. INTRODUCTION

Let me make immediately clear that my area is Business Administration, not - Technology. Therefore I look at the situation from a strictly economic point

of view. Due to this, I am not in the position to understand and even less LO

explain all the technical differences between the three membrane processes -

reverse osmosis (RO), ultrafiltration (UF) and electrodialysis (ED). However,

the literature seems to treat RO/UF as a concept and the material given to me

hardly mentions electrodlalysis. Therefore, hopefully with these liml tations

in your minds, allow me to speak generally cf membrane processes_ I think, or

at least hope, that if I make any statements rrhich are not correct from a - technical point of view, these will nrlt alter the ma;n points of my paper.

I regard my task to be to summarize the literature on membrane technoloz

and costs - which I will also do. However, I also take the opportunity towards

the end of this paper to give my professional critique on how economic calcu-

lations are generally made in the literature which I have covered.

I carry on with this paper around four themes, which will be treated in the

following order:

376 BJEEWE

- cal cul ations general ly made,

- inaustries investigated and reported,

- my critique,

- possibilities and limitations of membrane processes.

2. CALCULATIONS GENERALLY MADE

2.1 A remark

It is clearly impossible to give a calculation of membrane processes, which

is generally valid. One has to know the details in the individual case. Fac-

tors which among others will influence the result are

- the size and type of plant chosen,

- the flux, i-e. the rate of permeation through the membranes,

- the membrane used,

- rate of concentration wanted,

- the concentration of the feed.

Every liquid behaves differently. Also it is important to remember that

membrane techniques have existed not much more than one decade. The literature,

especially containing industrial applications, is very scarce, even sometimes

contradictory. The picture I give below is therefore a kind of “common denomi-

nator", an ideal picture. 1 look at membrane processes as systems and at the

same time trying to be inclusive as not too detailed.

2.2 Membrane processes as systems

It is easy to picture membrane processes in a ftow diagram - a feed meets

a membrane and separates jnto a concentrate and a permeate. To base an econ-

omic discussion only on this can be misleading. Each outgoing stream must be

processed further to obtain the desired final products_ The potential user

needs to know the total processing costs involved, whereas the equipment manu-

facturer often can provide only economic data concerning a specific unit oper-

ation.

Looking at membrane processes as systems the model should contain at least

the following components:

a)

b)

cl d)

el

Pretreatment.

Membranes.

Post-treatment.

Support systems, such as compressed air, cleaning subsystem, flushing

subsystem and instrumentation.

Acceptance tests of the streams.

BJEXKE 3T7

2.3 Costs ideally included

Below is given a list of costs that might be included In a specific calcu-

lation. This does not mean that they a17 have to be present every time a cal-

culation is made. The list could be regarded as a kind of check list. The

costs are divided into variable and fixed.

(i) Variable costs.

- Energy of all kind.

- Membranes (installation and replacement).

- Chemicals for cleaning and other purposes.

- Labour of all kind.

- Water.

- Supplies.

- Cost from leakage of solutes.

(ii) Fixed costs.

- Depreciation of major and auxiliary process equipment.

- Maintenance.

- Plant materials.

- Administrative expenses.

- Property taxes and insurances.

- Freight.

- Engineering and design services.

- Contingencies.

Nhat I list above as variable costs can sometimes be regarded as fl<ed and

vice versa. They can also sometimes be partly variable, partly fixed.

Parameters to characterize the performance of the system al so have to be

included, e.g. the rejection, yield and flux rate, which are pass 1 ble tempt-ane

performance measures and the ratio of the net added value of the concentrate

to the capital to be invested - a possible measure of the system as such.

The major parts to consider are usually those which at-e fixed such 3s

capital costs (sometimes over 50 Z) and variable such as energy, membranes an::

cleaning. The capital costs are directly proportional to the installed costs

of the concentration equipment, including costs of space and auxiliary equro-

ment such as storage tanks etc., they are directly prloortional LO the inter-

est and depreciation and are inversely proportional to the number of produc-

tive operation hours per year and the capacity of the concentration unit. The

main utility cost is that of energy. I order to allow cost comparisons that

are independent of rapidly changing values of currencies and of inct.easing

costs of fuel, energy consumptions are conveniently expressed in ste‘im eqdI;-

alents. Costs of membranes are ordinarily very crucial. For membrane processes

even sometimes more than 10 $A of operational hours might be required for

378 BJERKE

cleaning and maintenance_

2.4 Assumptions ideally included

In order to produce the calculations a lot of assumptions have to be known

in the individual case (besides those mentioned earlier), e.g.

- operating and cleaning hours,

- prices of all kinds,

- wages,

- chemical, thermical and mechanical conditions,

- life time of membranes and equipments,

- interest on capital,

- rate of inflation_

3- INDUSTRIES INVESTIGATED AND REPORTED

Examples of industries investigated and reported in the literature are:

3-f Dairies

Membrane processes are well-known in dairies and might replace evaporation

for many liquids, They are especially suitable in the following instances:

- Preconcentration of milk and whey.

- Fractloning of whey into protein and lactose constituents-

- In combination with evaporators.

3-2 Sewage wastewater

Results have been most encouraging, especially in smaller plants. Regula-

tions governing disposal of processing wastewaters, especially those high in

organic matter, have become more stringent in recent years. The ultimate dis-

posal technique might however have a large economic impact.

3.3 Pulp and paper mills

Membrane processes alone, or combined with freeze concentration, is quite

expensive_ Reduction of fresh water usage in the bleach plant and increased

membrane life could significantly lower the costs.

3-4 Desalination of brackish water

Membrane processes have developed rapidly for the desalination of brackish

waters and are in worldwide use. However, varying results are reported_

3.5 Tanning

Membrane processes provides tanners with a new option for meeting today's

effluent problems. They have demonstrated to be technically viable and econ-

BJ ERKE 379

omically favorable.

3.6 Soluble oil emu1 sions

Several plants are in operation and the savings in disposal pay back, some-

times only from credits given for the recycled and t-eutll ized fuel value of

the oil,

3.7 Electropaint recovery

Membrane processes can sidestep conventional ‘taste treatnenr: schemes for

t-ecoverlng the lost paint sol ids and returning them 1.0 the paint bath.

3.8 Potato processing trater

Enormous quantities of heavily pollhred \/ater at-e produced 111 the pro-

cessing of potatoes. The s’ituation is very similar to ;hat of cheese and so1-1?

membrane processes offer the potential of reducing the volume to be t:r-e3tenJ.

3-9 Chemltral manufacturivl

These are commercial appl ications where the only incentive IS to reduce

effluent disposal costs. One plant is reported, that wi th0ut a fT121ilSr*~n~

process probably have had to close dot/n because of the costs of effluent

disposal in an area conscious of the protection of the envit-onlrlent.

This is a sample of industrial apDlications_ IL has to DC sir-essed ‘chat the

economic advantages from using membrane processes somer,l;ws or-e t-epot-ted to he

very small _ Also, ner, calculations have to be made for f~cure indlviausl ap>l I-

cations. The vmes surrounding the use of such prXCSSGS 31-e SG:W. 1i”es v+z,-y

conrp 1 &X .

4. KY CRITIQUE

I would 1 Ike to point out a few matters which rn my op~nlon a?-e r'zi't'ly

considered in the literature:

(i) Start-up problems. Membrane processes are nw. ‘5cd.rt-up problems

must occur in many cases. These are rarely reported.

(ii) Performance measures. There are many ways ‘co measure the performance

of a membrane process system- These measures should ccme frw end users, not

from technicians in the system. - (iii) Structure of costs. The costs in the llt?t-atut-e are usually SETUC-

tured as averages. They can also be looked at as mat-gIna cr incremental

costs, which is more relevant in a step-rrize investment.

(iv) Theoretical and practical COSCS. Hany reports are based on theor-

etical calculations. In practice things are alilays more or less different.

(v) Rate of interest and life time of equipment. This is the most seri-

BJ ERKE

ous point- Capital costs in membrane processes are sometimes reported to be

3C or more_ I do not say it is done, but it is easy to manipulate the fig-

lA1-es on rate cf interest and life time of equipment, so that the result is

;zrled bettreen 0,6 - 1 ,4 of any figure. A check in any table of annuities can

confirm that! The assumptions behind these critical figures should therefore

x rnoroughly examined, rrhich 1s almost never the case- This is more serious

..?s ;‘nf eccnomic advantage of membrane processes sometimes is reported to be

Tar.; 1 rlal _

3. ?DSSIGILITtES AND l_If~lITATIOMS OF f~lEP1BRANE PRClCESSES

t?c I:w end by producing the oossibllities and limitations of membrane pro-

fesses as found in the 1 i teratut-c:

5. i Foss~b:litte~ p--L _ ::e?brane process plants give lorr energy costs,

- The process can remove th e water at low temperature and neutral pH.

- The pErmeat_t concentration is independent of feea concentration_ New

plants are unl likely to be based on a single pass system but \rould have

recirculation ;rhlch oould greatly increase flux rates_

- There should be no practical difficulties in operating membrane Dt-ocesses

in conJunction with conventional evaporators under commercial condltlons.

- The Process can be run either batch-rlize or continuously.

- Conscant tmprovements of membranes and fluxes are going on.

r c

-J _ - LilYi tat ions

- iitmorane life is critical to the economic efficiency- Sometimes even

t-ap1d, frecuent foul ing of the rxenbranes are reported_

- There are practical 1 icit ts for the concentration achievable.

- There are 1 imitations up\!ards in pressure, temperature and pH-values.

- rtigh maintenance and cleaning figures.

- IP comparison Lo evaporation, membrane processes are new techniques l:hich

?t-obably xi1 1 be aevelopcd further so the probabil ity that the equipment

~111 Ss obselete from a technological point of view is greater.

- Urlcertainry about the economic feasjbility of membrane processing has

Seep a principal factor inhibiting 1 ts rridespr-eaa adoption-

i?erlbrane technology i s nel:. Howeve)-, there are factors speaking for tk: ‘_ --

It wilt open new appt ication areas. Advances in membrane technology and pro-

cess design, increased enet-gy prices and more accurate care of the envi ronment

are perhaps the most important ones. Flembrane processes have come to stay.

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