Method for reducing the consumption of fresh water in a paper mill by means of a cooling tower

#The present invention relates to a method for reducing the consumption of fresh water and energy in a paper mill, in which fresh water is passed into the paper mill for various uses and a cooling tower is utilized for cooling water heated during the papermaking process.

#The present invention also relates to a cooling tower in which there is at least one inlet for passing the water to be cooled into the cooling tower, nozzles or equivalent for discharging the water that was passed in and that is to be cooled onto heat transfer faces, filler pieces and/or filler plates, which disperse the water to be cooled so as to increase the contact area between the water and the cooling air, at least one outlet for passing the cooled water out of the cooling tower, as well as blowers for blowing the cooling air through the cooling tower, whereby the air is heated as the water is cooled.

#In typical prior art paper mills, an abundance of fresh water is needed for cooling and for washing requirements in the wire part and the press section of the paper machine and for dilution in the pulp preparation plant.

#Additional objects of the invention will be apparent from the following description of the preferred embodiment thereof taken in conjunction with the accompanying non-limiting drawings, in which:

#FIG. 1 is a schematic illustration of the part of the papermaking process and its water circulations with which the cooling tower is connected;

#FIG. 2 is a sectional view of a cooling tower in accordance with the invention taken from the end of the tower;

#Referring to FIGS. 1-8B wherein like reference numerals refer to the same or similar elements, as shown in FIG. 1, fresh water is introduced into the water circulation of a cooling tower 100 associated with, e.g., a paper mill, along a duct 1. When used herein, a duct denotes not only a standard duct but also anything through which a flow is passed, e.g., a pipe. The rejects from the waters cleaned in the paper mill are brought along a duct S into a tank 97 to be fed into one or more evaporators 76 in which they are separated into steam, clean condensate and rejects. The rejects are removed from the evaporators 76 along a duct 98, and the steam passes through one or more cooling devices and/or one or more condensers 99 to condense and the condensed water is then directed into the cooling tower 100. In the condensers 99, concentrates and a warm water are formed. The concentrates from the condenser 99 or condensers are passed away along a duct 56. The clean condensate from the evaporators 76 is passed along a duct 80 into a warm water tank 87. The steam from the evaporators 76 passes into the condensers 99, to which cooling water is passed from the cooling tower 100. The temperature of the cooling water from the cooling tower 100 is regulated by means of a regulator 54. The water that became warm in the condensers 99 is passed into a top portion of the cooling tower 100 along a duct 101.

#In a preferred embodiment of the invention as shown in FIG. 1, fresh water is passed into a warm water tank 2 for fresh water along a duct 102 after passing through condensers 99. From the warm water tank 87, water is passed through a heat exchanger 88 into a hot water tank 89 along a duct 13', for example, to be used as jet water in the press section and in the wire part. Surface level regulators 103 and 104 in the tanks 2 and 87 operate jointly so that the supply of water into the tank 87 is secured and maintained. Any excess amount of warm water is passed to other uses. Part of the fresh water is, however, also passed directly into the warm water tank 87 along the duct 1. Warm water coming from the paper machine may also be directed into the warm water tank 87, also referred to herein as a buffer storage tank, and stored with the warm water from the condensers 99.

#FIGS. 2-7 are detailed illustrations of preferred exemplifying embodiments of the construction of a cooling tower 100 in accordance with the invention. The water Win to be cooled is passed in along ducts 10. The water to be cooled is sprayed or discharged in a downward direction through nozzles 13 or other comparable members. Above the nozzles 13, there is a so-called drop trap 14, by whose means passage of the cooling air directly upwards is prevented in order that the drops of the water to be cooled should become large enough and not pass out along with the air. The drop trap 14 can be disassembled readily and moved out of the way for servicing operations. The water to be cooled runs down along filler plates and/or pieces 15, by whose means a maximally large contact face is provided between the water flow, Win.fwdarw.Wout, to be cooled and the cooling air flow, Ain.fwdarw.Aout. The height of the space occupied by these filler plates or pieces 15 can be dimensioned so that a sufficiently long contact time and, thus, a sufficiently efficient cooling effect are obtained. The cooled water Wout comes out through a duct 17. In the cooling tower, at the outlet of the cooling air Aout, there is a noise attenuator and, moreover, sound insulation elements 19,19', which are arranged at the sides of the cooling tower. The sound insulation elements 19,19' also ensure that the cold air Ain comes from below, and thereby access of heated and moistened air back into the air circulation Ain.fwdarw.Aout is prevented. The function of a bottom basin 20 is to collect the cooled water after the cooling. Reference numeral 21 denotes wall and support constructions of the cooling tower. The blowers by whose means the cooling air Ain is blown into the cooling tower are denoted by reference numerals 23.