Method of pipe line washing

A method of pipe line washing is described, in which raw pulp liquid is washed by clean water or washing liquid having a lower concentration than liquid chemicals in the raw pulp liquid by making use of all or a part of a pipe line.

The present invention relates to a method of pipe line washing, in which 
digested pulp is washed with clean water to recover chemicals contained in 
the digested pulp. 
Although it has been known and practiced to recover chemicals contained in 
digested raw pulp liquid by washing the raw pulp liquid with clean water, 
the washing efficiency was not so high in the method of the prior art and 
hence a considerably large amount of clean water was necessitated for 
washing raw pulp liquid. 
It is therefore one object of the present invention to provide a novel 
method of pipe line washing in which a high washing efficiency can be 
attained with a minimum amount of clean water. 
According to one feature of the present invention, there is provided a 
method of pipe line washing in which raw pulp liquid consisting of a 
mixture of pulp and liquid chemicals, is washed with clean water or 
washing liquid having a lower concentration than the liquid chemicals in 
the raw pulp liquid by making use of all or a part of a pipe line, whereby 
clean pulp can be obtained.

Now the present invention will be described in greater detail in connection 
to one preferred embodiment thereof illustrated in the drawings. A general 
concept of the method according to the present invention is illustrated in 
FIG. 1, in which raw pulp liquid (31) consisting of a mixture of pulp and 
liquid chemicals introduced into a container (60) is made to sequentially 
flow through an alternate series of diluting pipes and concentrating pipes 
(E.sub.1.multidot.I, E.sub.1.multidot..PHI., E.sub.2.multidot.I, 
E.sub.2.multidot..PHI., --E.sub.i.multidot.I, E.sub.i.multidot..PHI., 
--E.sub.n+2.multidot.I, E.sub.n+2.multidot..PHI.), where i represents 
successive numbers 1, 2, 3, --, a suffix I means a diluting pipe and a 
suffix .PHI. means a concentrating pipe. 
Clean water or washing liquid (32) having a lower concentration than the 
raw pulp liquid is injected into the most downstream diluting pipe 
(E.sub.2+n.multidot.I) with respect to the flow of raw pulp liquid. In 
this diluting pipe (E.sub.2+n.multidot.I), the raw pulp liquid is diluted 
and in the concentrating pipe (E.sub.2+n.multidot..PHI.) located 
downstream thereof only the washing liquid is extracted. The washing 
liquid extracted from the concentrating pipe (E.sub.2+n.multidot..PHI.) is 
injected into the next upstream diluting pipe (E.sub.n+1.multidot.I) to 
dilute the raw pulp liquid having a higher concentration of liquid 
chemicals than the washing liquid in the (n+2)-th stage. Thereafter, again 
only the washing liquid is extracted from the concentrating pipe 
(E.sub.n+1.multidot..PHI.) located downstream thereof. 
The raw pulp liquid washed in the pipe line by repeating the 
above-mentioned operations has its concentration regulated in the stage 
(E.sub.D.multidot.I) at the downstream end, and the resultant clean raw 
pulp liquid (36) is transferred to the next step of the process. On the 
other hand, the washing liquid (34) is transferred from the first stage 
concentrating pipe (E.sub.1.multidot..PHI.) to the next step of the 
process. 
One example of the concentrating pipe (E.sub.i.multidot..PHI.) is 
illustrated in FIG. 2, and one example of the diluting pipe 
(E.sub.i.multidot.I) is illustrated in FIG. 3. At first, referring to FIG. 
2, raw pulp liquid (40) has only washing liquid (40) therein passed 
through a trainer provided in a pipe (51) (slits or holes being opened in 
the pipe (51)) and flows towards the downstream end as raw pulp liquid 
(42) having a higher pulp concentration. It is to be noted that in these 
figures, reference numeral (50) designates flanges, numeral (52) 
designates a washing liquid reservoir, and numeral (53) designates in FIG. 
2 an extraction port for washing liquid but it designates in FIG. 3 an 
injection port for washing liquid. 
In a diluting pipe shown in FIG. 3 such as, for instance, the diluting pipe 
(E.sub.n+1.multidot.I), raw pulp liquid (43) supplied from the 
concentrating pipe (E.sub.n.multidot..PHI.) in the preceding stage flows 
into the pipe (51) associated with a trainer, washing liquid (41) 
extracted from the concentrating pipe (E.sub.n+2.multidot..PHI.) in the 
next downstream stage flows into the piping (51) through the injection 
port (53) as shown at (44), and diluted raw pulp liquid (45) flows out of 
the diluting pipe (E.sub.n+1.multidot.I) to the downstream concentrating 
pipe (E.sub.n+1.multidot..PHI.). 
FIG. 4 shows an installation in which the method according to the present 
invention is practiced. In this installation, chips of wood (30) are 
passed through a rotary valve (1) and then introduced into a continuous 
digesting apparatus (2) containing liquid chemicals and maintained at a 
high temperature and at a high pressure to be subjected to digesting 
effect, and thereby they are pulped. The pulp (31) produced as a result of 
pulping falls into a cooling tank (3) while being associated with liquid 
chemicals, and after it is cooled and diluted by diluting liquid (33) 
supplied through a line (8), it is extracted externally of the system and 
transferred to a drum washing apparatus in the next step of the process. 
During the above-mentioned process, clean water or washing liquid (32) 
having a lower concentration than the liquid chemicals in the raw pulp 
liquid is injected into a diluting pipe (5) through a line (10) to dilute 
the raw pulp liquid. The diluted raw pulp liquid has only the washing 
liquid extracted from a concentrating pipe (6), the raw pulp liquid (36) 
having its pulp concentration raised is passed through a line (7) as being 
washed, and then it is transferred to the next step of the process. 
The diluting liquid extracted from the concentrating pipe (6) passes 
through a line (11), then joins with the diluting liquid (33), and is fed 
to the cooling tank (3) through the line (8) to be used for diluting the 
raw pulp liquid. The washing liquid contained in the raw pulp liquid 
diluted in this cooling tank (3) is extracted from a concentrating pipe 
(4) through a line 9 as washing liquid (34) collected after washing, and 
then transferred to the next step in the process. In this way, the pulp 
(31) is subjected to washing effect in the pipe line, and made into clean 
raw pulp liquid (36). 
As described above, the present invention is practiced in the following 
mode. That is, the system is constructed of pipe lines, diluting pipes and 
concentrating pipes, and after clean water or washing liquid having a 
lower concentration than the liquid chemicals in the raw pulp liquid has 
been injected into an arbitrary diluting pipe (E.sub.n+2.multidot.I) shown 
in FIG. 1 to dilute and mix with the raw pulp liquid, only the washing 
liquid is extracted in the downstream concentrating pipe 
(E.sub.n+2.multidot..PHI.). Then the washing liquid extracted from the 
concentrating pipe (E.sub.n+2.multidot..PHI.) is injected into the 
upstream diluting pipe (E.sub.n+1.multidot.I) having a higher 
concentration than the liquid chemicals in the raw pulp liquid which has 
been partly washed in the (n+2)-th stage, and again only the washing 
liquid is extracted from the downstream concentration pipe 
(E.sub.n+1.multidot..PHI.). After the raw pulp liquid has been washed in 
the pipe line by repeating such operations, it is subjected to 
concentration regulation at the downstream end of the washing and then 
transferred to the next step of the process. On the other hand, the 
washing liquid collected after washing is also transferred to the next 
step in the process as maintained in the condition where the concentration 
of the liquid chemicals has been most increased. 
As described in detail above, according to the present invention, raw pulp 
liquid consisting of pulp and liquid chemicals is washed with clean water 
or washing liquid having a lower concentration than the liquid chemicals 
in the raw pulp liquid by making use of all or a part of pipe line, hence 
the washing can be achieved in a pipe line, and therefore, a volume of the 
drum cleaning apparatus in the prior art can be reduced and, as a whole, 
the system can be made compact. Also, in the case where a drum washing 
apparatus has been already installed and it is desired to increase the 
washing capability of the system, if the method according to the present 
invention is employed, then reconstruction and/or rearrangement of the 
washing system can be made minimum.