Patent GB-698190-A (GB)
Title: Improvements relating to ion-exchange plants
Inventor: SARD BERNARD ABEL
IPC: C02F1/42
Filed: 1950-11-28
Abstract: 698,190. Electric tests and measurements, PERMUTIT CO., Ltd. Nov. 19, 1951 [Nov. 28 1950; Jan. 15, 1951], Nos. 29123/50 and 1106/51. Class 37. [Also in Group I] In an ion-exchange plant for producing acidfree water, means are provided for comparing the electrical conductivity of the water which should be acid-free with that of the same water after passing through a bed of cation-exchange material charged with basic cations and a signal is given when as a result of the water not being acid-free a difference in conductivities is produced. Where the acid-free water is a blend of acid, water from a bed of cation-exchange material charged with hydrogen ions and of alkaline water, some of the acid water may be passed through an auxiliary bed of cationexchange material charged with basic cations, and means are provided for comparing the electrical conductivity of the effluent from such an auxiliary bed with that of the blended water and for indicating the difference between these conductivities ; this procedure provides for indicating the amount, if any of bicarbonate alkalinity in the mixed effluent. Raw water supplied through a pipe 1 is divided into two streams, one of which passes through a bed 4 of cation-exchange material charged with hydrogen ions, the effluent 6 thus being acid, and the other of which passes through a bed 5 of cationexchange material charged with sodium ions, the resulting effluent 7 thus being soft water with its original bicarbonate alkalinity unchanged. The effluents are blended by a valve system 8, the water flowing to service at 19 being required to be acid-free ; the blend may, however, have a small residual bicarbonate alkalinity. A fraction 10 of the blended water passes to a conductivity cell 11 in the common arm of a double Wheatstone bridge network, while a further fraction passes through a small auxiliary bed 13 containing cation-exchange material charged with basic cations, the effluent therefrom flowing through a conductivity cell 15 in the right-hand arm of the network. The right-hand bridge comprising cells 11 and 15 and the galvanometer between them is arranged to be balanced when the conductivities in the cells are equal. Thus, if the blended water from 8 becomes acid, the acidity in the fraction of it passing through bed 13 will be replaced by basic cations in that bed and the effluent therefrom will be less acid and therefore less conducting. The loss of balance will be indicated and the resulting current may be used to initiate automatically an appropriate re-setting of the valve-system 8. This part of the plant is analogous to that disclosed in Specification 624,884, referred to in the first Provisional Specification. A fraction of the acid effluent is conducted through a second auxiliary bed 17 containing cation-exchange material charged with sodium ions; the effluent from it will thus be free from bicarbonate alkalinity (the influent being acid and thus free from bicarbonate alkalinity) and will contain the original sulphates and the like as sodium salts, and will accordingly represent in composition properlytreated blended water. The electrical conductivity of this effluent is compared, by means of the cell 18 in the left-hand arm of the double Wheatstone bridge network, with that of the blended water passing through the cell 11, and the valve-system 8 is maintained adjusted, preferably automatically, so that the conductivity in the cell 11 is as close as possible to that in the cell 18 and never exceeds it by more than a small predetermined amount. Such excess conductivity when present indicates a greater alkalinity in the main effluent 19 than in the auxiliary " ideal " effluent from the bed 17. The over-riding control is arranged to be the first one described above to obviate the production of an acid effluent. Specification 497,943, [Group I], is referred to as disclosing one method of producing an acid-free water from a single bed.