WO1983001579A1

WO1983001579A1 - Evaporating procedure and apparatus

Info

Publication number: WO1983001579A1
Application number: PCT/FI1982/000056
Authority: WO
Inventors: Oy Mkt-Tehtaat; Heimo Välimäki
Original assignee: Mkt Tehtaat Oy
Priority date: 1981-11-10
Filing date: 1982-11-10
Publication date: 1983-05-11
Also published as: FI63680B; SE8303898D0; DK318283D0; DE3249168C2; NL8220411A; DK151182C; DK151182B; SE8303898L; FI63680C; DE3249168T1; DK318283A

Abstract

Procedure and apparatus for carrying out evaporation in at least two successive evaporators (1, 2) connected in series. In the evaporation, heating steam is used, which most appropriately at least in its main part consists of that vapour which separates from the liquid that is being evaporated, in connection with the evaporating process. The heating steam supply duct system (6-11) has been provided with at least two blowers (12, 13) which have been so connected in series that one of them constitutes the main blower (12), connected by ducts (8, 9) on one hand to the first evaporator (1) in the series and on the other hand to the second blower (13) serving as auxiliary blower, and that the auxiliary blower has been connected by a duct (10) to the latter evaporator (2) in the series. The auxiliary blower (13) is substantially smaller in size than the blower (12), and the controlling of the process can be effected exclusively with the aid of the control means attached to the auxiliary blower, whereby the total energy consumption of the process is reduced and accurate control of the solid matter content of the end product from the evaporating step is enabled.

Description

Evaporating procedure and apparatus

The present invention concerns an evaporation procedure wherein the evaporation is carried out using at least two successive evaporators connected in series with regard to the liquid that is being evaporated and wherein this liquid is heated with steam which is introduced in the evaporators from a duct system provided with at least two blowers or equivalent pieces of equipment increasing the pressure of the steam.

Such evaporating procedures are known in the art wherein the liquid to be evaporated is conducted through successive evaporator units so that the evaporating temperature and the solid mtter content of the liquid increase by steps. It is possible to use for heating steam the vapour that separates from the liquid that is being evaporated, the pressure and temperature of this vapour being increased with the aid of blowers, compressors or equivalent apparatus.

Problems are caused in evaporation processes by the fact that the efficiency of the process tends. to go down with time, owing to soiling of the evaporators. As the solid matter content of the inspissated product should be constant, the drop in evaporating efficiency must be compensated by adding to the lifting height of the blowers. It is however a fact that any regulating means attached to the blowers increase their energy consumption, in addition to which the regulation should be exceedingly precise, since even a minor change in the amount of liquid evaporated causes a comparatively great change in the concentration of the inspissated product. For this reason difficulties have been encountered in practice in keeping this concentration constant.

The object of the present invention is to provide an evaporating procedure in which the problems mentioned have been largely avoided. The invention is characterized in that the heating steam blow ers are used in series connection so that one of them operates as main blower, part of the steam that has passed therethrough being conducted to the first evaporator in the series and another part, to a blower serving as auxiliary blower, from which the steam is conducted to the latter evaporator in the series.

In the design solution of the invention, in which the main blower may be substantially bigger than the auxiliary blower, it is not absolutely necessary to regulate the main blower during the process at all, instead of which all regulating measures may be directed on the auxiliary blower. This obviates the necsssity of mounting expensive regulating gear on the main blower, and it will also cause no extra energy consumption in the process. Owing to the smaller size of the auxiliary blower, the mounting of regulating means on this unit is less epxensive, and since also the amount of energy consumed by the auxiliary blower is less, it will not considerably increase the total energy consumption in the process, even at poorer efficieny, if such were the case. The small-sized auxiliary blower can also be regulated rather closely so that the desired solid matter concentration is exactly attained in the ultimate inspissated product.

The invention further concerns an apparatus for carrying out the procedure just described. This apparatus comprises in a way in itself known in the art, at least two successive evaporators connected in series with regard to the liquid that is being evaporated, and a duct system through which heating steam is supplied to the evaporators and which has been provided with at least two blowers or equivalent pieces of equipment increasing the steam pressure. The apparatus is characterized in that the blowers have been connected in series so that one of them constitutes the main blower, connected by means of ducts, on one hand, to the first evaporator in the series and, on the other hand, to the second blower serving as auxiliary blower, and that the auxiliary blower has been connected by means of a duot to the latter evaporator in the series. The invention is described in the. following in greater detail with the aid of an example, with reference to the attached drawing, presenting an evaporation apparatus according to the invention.

The apparatus depicted in the drawing comprises two successive evaporators 1 and 2 connected in. series and through which the liquid to be evaporated, passing along the conduits 3, 4 and 5, is conducted. The evaporation is effected by means of steam, this steam being mostly made up of the vapour which separates from the liquid to be evaporated, in the evaporators 1 and 2. This steam obtained from the liquid that is being evaporated is removed from the evaporators 1 and 2 into the ducts 6 and 7 and further conducted through the ducts 8, 9 and 10 as heating steam back to the evaporators. With the duct 7 connects the duct 11, through which it is possible to carry into the apparatus external steam to maintain the thermal equilibrium. The duct system 6-11 has been provided with two blowers 12 and 13, by which the pressure and temperature of the heating steam are increased in requisite degree. The blower 12 in duct 8 operates as main blower, through which passes all the heating steam used towards evaporating. The main part of this steam is conducted to act as heating steam, to the first evaporator 1 in the series, and the remainder is conducted through the duct 9 to the blower 13 serving as auxiliary blower, and thence further through the duct 10 to becomme heating steam, to the latter evaporator 2 in the series. The condensate formed of the heating steam is removed from the evaporators 1 and 2 into conduits 14 and 15.

In the apparatus here presented, the power rating of the auxiliary blower 13 may be on the order of 1/10 to 1/5 of the rating of the main blower 12. The main blower 12 is arranged to operate under optimum conditions, and it is not regulated during the evaporation process, for which reason it need not be provided with energy-consuming regulating means. The drop of evaporating efficiency taking place during the process owing to soiling of the evaporators 1 and 2 is exclusively compensated for by regulating the auxiliary blower 13, and to this purpose the auxiliary blower is provided with inverter, guide vane controller or equivalent lifting height regu lating means. Since the principal part of the evaporation takes place in the first evaporator 1 of the series and only a minor part of the heating steam goes through the auxiliary blower 13, the regulating means of the auxiliary blower have no substantial influence on the total energy consumption of the process. The control of the auxiliary blower 13 may in the case of high evaporating ratios be based on measurement of the end product density, and as a result of the high accuracy of control, higher than before solid matter concentrations are reached in the end product.

Among the applications of the invention may be mentioned as example the pretreatment, before the drying step, of whey used towards producing whey powder: this may take place e.g. in a spray tower dryer. In such pretreatment, the solid matter content of the whey is increased from 6 to 60%, using for instance two successive evaporators, of which the first raises the solid matter content to about 20%. In such a process, the main blower may have a power rating about six times that of the auxiliary blower, and the process may be so dimensioned that the external heating steam required is at most a few per cent of the total amount of heating steam.

It is obvious to a person skilled in the art that different embodiments of the invention are not confined to the example just presented and may rather vary within the scope of the claims following below.

Claims

1. Evaporating procedure, wherein the evaporation is carried out using at least two successive evaporators (1,2) connected in series with regard to the liquid that is being evaporated and wherein the liquid to be evaporated is heated with steam which is carried to the evaporators from a duct system (6-11) provided with at least two blowers (12, 13) or equivalent means increasing the pressure of the steam, characterized in that the blowers (12, 13) are operated connected in series so that one of them operates as main blower (12), part of the steam that has gone therethrough being conducted to the first evaporator (1) in the series and another part to the second blower (13), which serves as auxiliary blower, whence the steam is conducted to the latter evaporator (2) in the series.

2. Procedure according to claim 1, characterized in that the solid matter content of the end product is maintained constant during the evaporation process by controlling the lifting height of the auxiliary blower (13).

3. Procedure according to claim 1 or 2, characterized in that as heating steam is used vapour separating from the liquid that is being evaporated.

4. Apparatus for carrying out a procedure according to any one of the preceding claims, this apparatus comprising at least two successive evaporators (1, 2) connected in series regarding the liquid that is being evaporated, and a duct system (6, 11) through which heating steam is carried to the evaporators and which has been provided with at least two blowers (12, 13) or equivalent means increasing the steam pressure, characterized in that the blowers (12, 13) have been connected in series so that one of them constitutes a main blower (12) which has been connected by ducts (8,9), on one hand, to the first evaporator (l) in the series and, on the other hand, to the second blower (13) serving as auxiliary blower, and that the auxiliary blower has by a duct been connected with the latter evaporator (2) in the series.

5. Apparatus according to claim 4, characterized in that the auxiliary blower (13) has been provided with inverter, guide vane controller or equivalent means for controlling the blovrer's lifting height.