Optimization of Technological Water Consumption for an Industrial Enterprise with Self-Supply System

Transcription

1 , March 13-15, 2013, Hong Kong Optmzaton of Technologcal Water Consumpton for an Industral Enterprse wth Self-Supply System Ioan Sarbu, Gabrel Ostafe and Emlan Stefan Valea Abstract Modern ndustry uses large quanttes of water for producton processes and requrement to water qualty s hgher and hgher. Technologcal water supply of few ndustral enterprses often put complcated ssues n terms of consumpton to users. In ths artcle s developed a numercal smulaton model of technologcal water consumpton for an enterprse n chemcal sector wth self-supply system. Based on ths smulaton model a computer program was elaborated n FORTRAN programmng language, whch s expected to be mplemented n a computer control and montorng centralzed system. The results of ths program are used to takng decsons that ensure optmal operaton of the system wth a hgh relablty and wth low energy consumpton, takng nto account the operaton dynamcs of enterprse water users. The numercal results of a practcal applcaton for studed ssue show the operatonal effcacy of proposed smulaton model. Index Terms water supply, ndustral enterprse, technologcal consumpton, numercal smulaton model, computer program. I. INTRODUCTION ATER supply n ndustral sector s an mportant task Wof the natonal economes, because modern ndustry uses large quanttes of water for producton processes and requrement to water qualty s hgher and hgher. It s estmated that 22% of worldwde water s used n ndustry. Maor ndustral users nclude hydroelectrc dams, thermoelectrc power plants, refneres, manufacturng plants, and other chemcal plants. In these ndustral sectors, large volumes of treated water are nvolved n the producton process. Industry requres pure water for many applcatons and utlzes a varety of treatment technques both n water supply and dscharge [1], [2]. Dmnshng qualty water supples, ncreasng water purchase costs, and strct envronmental effluent standards are forcng ndustres to target ncreased water-effcency and reuse. These factors, n combnaton wth an estmated fvefold ncrease n I. Sarbu s wth the Department of Buldng Servces, Poltehnca Unversty of Tmsoara, Tmsoara, Romana (correspondng author to provde phone: ; fax: ; e-mal: oan.sarbu@ ct.upt.ro). G. Ostafe s wth the Department of Buldng Servces, Poltehnca Unversty of Tmsoara, Tmsoara, Romana (e-mal: gabrel.ostafe@ct.upt.ro). E. S. Valea s wth the Department of Buldng Servces, Poltehnca Unversty of Tmsoara, Tmsoara, Romana (e-mal: emlan.valea@ct.upt.ro). worldwde manufacturng water use by 2030, wll contrbute to growng ndustral water/related expenses n the near future [3]. In 1995, the estmated water use for all domestc ndustres was m 3 /day, and currently the global annual cost to purfy ndustral-use water and wastewater exceeds $ 350 bllon [4], [5]. Water for ndustral use may be delvered from a publc suppler or be self-suppled. For establshng water supply system n ndustry and the network scheme [6] s necessary to take nto account the condtons of unnterrupted users supply wth mnmum energy consumpton. These are necessary for achevng planned producton, and for avod equpments damage. Thus, wthn many ndustral enterprses s adopted technologcal water supply self-system wth recrculaton. Snce technologcal water supply of such ndustral enterprses often put complcated ssues n terms of consumpton to users, so t s necessary both systematc analyss of the flow and pressure dstrbuton n system and optmzaton [7]-[9] of the users water consumpton by a computer control and montorng centralzed system. In [10] s presented a computatonal model for the analyss and operaton optmzaton of a recycled technologcal water network. In ths artcle s developed a numercal smulaton model of technologcal water consumpton for an enterprse n chemcal sector wth selfsupply system. Based on ths smulaton model a computer program was elaborated, whch s expected to be mplemented n a computer control and montorng centralzed system. The results of ths program are used to takng decsons that ensure optmal operaton of the system wth a hgh relablty and wth low energy consumpton, takng nto account the operaton dynamcs of enterprse water users. II. MERICAL SIMULATION MODEL OF TECHNOLOGICAL WATER CONSUMPTION It s consdered the self-system of an ndustral enterprse suppled wth natural water from surface source. The prncple scheme of the system s shown n Fgure 1. Wthn of ths system are the followng qualty categores of technologcal water: fltered (decanted) water; chlled fltered water whch s recycled; softened water; demneralzed water. Also, the system comprses the followng user categores: drect users, those who consume fltered water, ndrect users, those who use water ether after addtonal treatment or through recrculaton. In Fgure 2 s shown a scheme of water ensurng to users, whch ncludes pumpng

2 , March 13-15, 2013, Hong Kong statons correspondng to each step of the system. The coeffcents k p and k s takes nto account the water losses n system and respectvely the system self-consumpton. Fg. 1 Scheme of technologcal water supply system C water catchng; SPI, SPII, SPIII I, II, III stage pumpng staton; ST natural water treatment staton; I storage; D dstrbuton network; U user Fg. 2 Scheme of water supply to users Proposed numercal model for computer-aded smulaton of technologcal water consumpton nvolve the establshment of technologcal water quanttes n system sgnfcant sectons. These sectons represent users, storage, treatment plant and catchng. There are consdered known followng basc data: hourly producton and specfc consumpton per unt of product, on water qualty categores, for each user; duraton of daly producton for each user; volume and restoraton tme of ntangble fre reserve; maxmum capacty of treatment plant. Water demand of users represents the water quantty to be provded at use ponts, so that technologcal processes to be effcent satsfed. Ths s determned on bass of adopted producton technologes, dependng on the hourly producton and the specfc dscharge per product unt, for each qualty category of water. Water requrement of users represents the water quantty to be taken from the source to satsfy effcent the water demand, water losses n the system and ts domestc consumpton, wth optmal reuse or recrculaton wthout dmnsh producton. Water requrement s determned per hours and for water qualty categores, as follows: f, k p k s q f P t, (1) m, k p k s qm P t, (2) d, k p k s qd Pt, (3) t0 r, k p k s qr P t, (4) t (5), f, m, d, r, u o fu (6) fu 1 1 f, (7) mu 1 m, (8) du 1 d, (9) ru mu r, (10) fo 1 mo 1 do 1 1 d du f ru, (11) m, (12), (13) ro r, (14) (15) fo mo where: k p s the coeffcent of water losses n system, k s coeffcent that takes nto account the self-consumpton of system; q f, q m, q d, q r specfc consumpton for user of fltered, demneralzed, softened and recycled water, P hourly producton of user ; τ, tme varable wth the value 0 or 1 as n the hour a gven user consumes water or not; Δt 0, Δt nomnal and real temperature dfference of recycled water to user ; f,, m,, d,, r,,, respectvely, the fltered, demneralzed, softened, recycled and fully treated water quantty, requested at hour by user ; fu, mu, du, ru, u respectvely, the fltered, demneralzed, softened, recycled and fully treated water quantty, requested by the user ; fo, mo, do, ro, o respectvely, the fltered, demneralzed, softened, recycled and fully treated water quantty, requested at hour by the users. The determnaton of water consumpton on hours and users offer the possblty know t for each user both on technologcal water qualty categores and global. It s possble also to know consumpton daly varaton, on qualty categores and global, allowng calculaton of the hourly varatons percentage of consumpton: o k (16) 1 and of the natural water dscharge necessary to be captured from source: do o ro k, (17) c s 1 u Ths, f smulaton s performed for a fre case, gets the form:

3 , March 13-15, 2013, Hong Kong V c k u T s 1 r (18) where: s the number of water users; V water volume of fre ntangble reserve; T r fre water reserve recovery tme. Snce the technologcal water demand n system s suppled through storage tanks whch are servced by pumpng statons, s determned ther fluctuant volume for a perod of one day ( hours), usng the cumulated dfferences analytcal method [6]. The value of requred useful volume for storage tanks s gven by equaton: Vu V f Vnt (19) n whch V nt = 0.1 c represents water volume for technologc needs of the system. Assumng normal operaton of the enterprse supply system, useful volume V u needed for storage s equal to the exstng useful volume V 0 acheved by storage buldng. Also, maxmum capacty MAX of the treatment plant at a gven turbdty of natural water s at least equal to captured water dscharge, whch determnes the volumev 0. When n supply system operaton there are devatons from the normal water dscharges, appear two runnng dstnct stuatons for storage tanks: a) When V u < V 0 : f c MAX, (20) begnnng wth start tme of water storage n the tank, t could be reduced captured natural water dscharge by value: V0 Vu c (21) T n whch: T s perod of tme snce water accumulaton n storage tanks untl reachng the fluctuant volume; f c MAX, (22) are ntroduced constrants to users, ther needed reducton of water consumpton Δ UT s gven by: c MAX UT (23) k s b) When V u > V 0 : f s accomplshed condton (20), storage tanks operate only as sucton basn of water pumpng staton n the dstrbuton network; f s verfed nequalty (22), s necessary ntroducton of constrants to users, ntal reducton of ther water consumpton: Vu V 0 UT, () 2 beng determned through successve approxmatons so achevng the condton: V u V 0 ε (25) n whch ε (0.5 2 m 3 ) s the admssble error n useful volume calculaton If nequalty (22) s stll mantaned are ntroduced more severe restrctons, reducng water consumpton of the users wth the value gven by relaton (23). For each user to whch s allowed hourly producton dmnshng (ψ = 0), t s necessary to reduce ts technologcal water consumpton wth: u u R UT (26) u 1 1 u Correspondng hourly producton becomes: P' ψ P (27) where: u ψ 1, (28) u and R represent water user s number whch not allow supply constrants. It s regenerated calculaton of hourly water consumpton for users under the created constrants. III. COMPUTER PROGRAM SIOCATEH Based on the computatonal model developed above a computer program SIOCATEH was elaborated n FORTRAN programmng language for PC compatble mcrosystems. Ths program operates sequentally by callng sx subroutnes and haves flow chart n Fgure 3. As nput parameters are ntroduced: general data:, V 0, MAX, k p, k s, ; V, T r ; consumpton tmes for each user durng the day τ(i,j); characterstcs of water users: P(J), q f (J), q m (J), q d (J), q r (J), Δt 0 (J), Δt(J), ψ(j). For the dentfer ψ(j) s assgned ntal value 0 or 1 as J user s allowed or not to decrease the producton. Accuracy of acheved results s a functon of the nput data accuracy, as the hourly producton and specfc water dscharge per product unt (pu). IV. MERICAL APPLICATION For example are presented four sgnfcant assumptons whch may occur n the operaton of a water supply system for sx technologcal users wth contnuous operaton durng the day and wth the characterstcs provded n Table I. These hypotheses are the followng: TABLE I CWATER USERS CHARACTERISTICS User P q f q m q d q r Δt 0 Δt [pu] [m 3 /hpu] [m 3 /hpu] m 3 /hpu] [m 3 /hpu] [K] [K] Ψ

4 , March 13-15, 2013, Hong Kong Fg. 3 Flow chart of computer program SIOCATEH ) Consderng V 0 = m 3 and MAX = m 3 /day, was obtaned a requred useful volume of storage V u =11001 m 3, from a total users consumpton of treated water u = m 3 /day. So, t results a reducton Δ UT = m 3 /day of user consumpton, whch leads to decrease of ther hourly producton n proporton ndcated by coeffcents ψ. In ths stuaton t s necessary to capture the natural water dscharge c = m 3 /day. ) The values V 0 = m 3 and MAX = m 3 /day are assumed. Snce has resulted V u = m 3 < V 0, begnnng on moment that water s stored n tanks, t could be reduced captured water dscharge c = m 3 /day wth value Δc = 37.8 m 3 /h on a perod T = hours, obtanng 0 = m 3 /day wthout affectng nomnal producton of users. ) It are consdered values V 0 = m 3 and MAX = m 3 /day, and has resulted V u = m 3 > V 0, beng so possble the catchment of necessary natural water dscharge c = m 3 /day < MAX, wthout ntroducng constrants at users. ) Assumng values V = 2000 m 3 and T r = hours, along parameters of hypothess (), t was determned technologcal water consumpton after a fre and have resulted as necessary the followng values: V u = m 3, c = m 3 /day, Δ UT = m 3 /day. Consequently, there s need of more strngent constrants at users than for hypothess (), because of necessty catch an addtonal natural water dscharge for the recovery of fre ntangble reserve. The computaton was performed wthn the lmts of precson = 0.5 m 3. Table II summarzes the fnal results obtaned only for the total treated water consumpton, for each user, correspondng of each consdered hypothess. V. CONCLUSION The storage operaton depends on daly water consumpton and s determned by hourly varaton of t. Based on the dfference between real and calculated useful volume s optmzed operaton of technologcal water supply system. Dfference of useful volume remaned n the storage tank can be valued by reducng water dscharge captured over a correspondng perod. In ths way t s saved electrcty and reagents for the treatment plant.

5 , March 13-15, 2013, Hong Kong TABLE II TOTAL TREATED WATER CONSUMPTION FOR EACH USER Hypothess User () () () () u [m 3 /day] ψ u [m 3 /day] u [m 3 /day] u [m 3 /day] ψ Total c [m 3 /day] V u [m 3 ] Global technologcal water consumpton of enterprse s lmted by the maxmum treatment capacty of related facltes. Ths s a functon of avalable water turbdty n source. After any eventual water consumpton for fre, the source ensure water dscharge necessary for the recovery of fre reserve, mposng n most cases constrants for water-users. The proposed numercal smulaton model offers the advantage of an operatonal calculus, s programmable on mcrosystems, has a hgh degree of generalty, and can be appled to varous ndustral enterprses wth technologcal water self-supply system. Computer program SIOCATEH s very sutable to be mplemented n a centralzed montorng and control system of technologcal water consumpton. Ths system could be optmzed water supply for technologcal facltes, elmnatng water wastage, ncreasng relablty, reducng reagent consumpton fees for water treatment and savng electrc energy. REFERENCES [1] G. Tchobanoglous, F. L. Burton, and H. D. Stensel, Wastewater Engneerng, New York, McGraw-Hll, [2] Gh. Morar, Contrbutons to economcal and techncal solvng of water ndustral treatment processes, Ph.D. dssertaton, Techncal Unversty of Cvl Engneerng Bucharest, Bucharest, Romana, [3] W. Royal, Hgh and Dry, Industry Week, vol. 9, no. 15, pp.-30, [4] W. B. Solley, R. R. Perce, and H. A. Perlman, Estmated Use of Water n the Unted States, Washngton D.C., U.S. Government Prntng Offce, [5] L. Yamanda, Market Magc: Rdng the Greatest Bull Market of the Century, New York, John Wley & Sons, [6] A. Manescu, M. Sandu and O. Ianculescu, Water Supply (n Romanan), Bucharest, Teachng and Pedagogcal Publshng House, [7] A. B. Sakarya and L. W. Mays, Optmal operaton of water dstrbuton pumps consderng water qualty, Journal of Water Resources Plannng and Management, vol. 126, no. 4, pp , [8] M. Rafrou, Smulaton Models n Cvl Engneerng (n Romanan), Tmsoara, Facla Publshng House, [9] E. Polak, Computatonal Methods n Optmzaton, New York, Academc Press, [10] I. Sarbu, Analyss and optmzaton model of recycled technologcal water supply network, Cvl Engneerng, no. 8/9, 1987.