METHOD AND APPARATUS FOR CLEANING THE TUBES OF A TUBU- LAR HEAT EXCHANGER The present invention relates to a method as defined in the preamble of claim 1 and to an apparatus as defined in the preamble of claim 4 for cleaning the tubes of a heat exchanger. In particular, the method and apparatus of the invention relate to the cleaning of the heat exchanger tubes of calorisators comprised in a pulp digestion process and those of the evapora- tor equipment used in the circulation of chemicals.

In the chemical woodworking process, calori- sators are generally used for heat recovery in connec- tion with pulp digestion, and evaporators are used for the vaporization of water in black liquor in the chemical circulation. The structure of these devices is typically so implemented that hot pure steam is supplied into the cylindrical part of the heat ex- changer of the device, outside the heat exchanger tubes. The alkaline cooking liquor is fed into the heat exchanger tubes via the end calottes of the heat exchanger. Heat exchange occurs while the liquor is flowing through the tubes. The alkaline cooking liq- uor, which in the heat exchangers is the liquid flow- ing inside the heat exchanger tubes, contains ingredi- ents that are apt to develop pitch and stick fast on the interior surface of the heat exchanger tubes.

Typical problems with the heat exchangers are clogging of the tubes due to the formation of pitch and impairment of heat transfer capacity due to soil- ing. To maintain the functionality of the heat ex- changer, the tubes have to be cleaned at regular in- tervals, after which the heat transfer properties are almost like those of a new heat exchanger. However, the result essentially depends on the quality of the cleaning work.

In a prior-art method, heat exchanger tubes are cleaned by drilling. By this method, a completely blocked tube can be opened. By choosing an appropriate drill size, it is possible to remove almost all impu- rities from the wall of the tube. However, there is the risk of damaging the tube. In long tubes, the drilling can easily be done in a somewhat skewed di- rection, and this may result in a hole in the tube wall or at least a substantial reduction of the wall thickness in a given portion of the tube. This may lead to a breakage of the tube at some later time.

Another known method is to use pressure wash- ing for cleaning the tubes. However, this method in- volves the problem of poor cleaning efficiency. This type of technique is proposed e. g. in the patent US 4025362. As the washing fluid is forced into the spaces between the heat exchanger tubes or lamellas from above the structure, the nozzles do not work properly in the small gaps and spaces, but the spaces being filled with water and loosened impurities sig- nificantly reduce the cleaning efficiency.

The object of the invention is to eliminate the above-mentioned drawbacks. A specific object of the invention is to disclose a new type of method and apparatus by means of which the heat exchanger tubes of tubular heat exchangers can be cleaned in a manner as simple and quick as possible and without damaging the tubes in any way, so as to render them equal to new heat exchangers in respect of their heat transfer capacity.

As for the features characteristic of the in- vention, reference is made to the claims.

In the method of the invention, in order to clean the substantially vertical heat exchanger tubes of a tubular heat exchanger internally, a washing hose with a nozzle at its end is inserted into the heat ex- changer tube from below and pushed upwards. The hose

and the nozzle are rotated while being pushed into the tube, and likewise during the pushing movement a high- pressure jet of washing fluid at over 100 MPa is dis- charged from the nozzle onto the interior surface of the heat exchanger tube.

During the cleaning operation, the hose and nozzle are preferably moved by means of a separate feed device in the longitudinal direction of the tube being cleaned and the hose and nozzle are rotated by a separate rotator. The feeding power for the feed de- vice is preferably taken from the rotary motion of the hose.

The apparatus of the invention for internal cleaning of substantially vertical heat exchanger tubes of a tubular heat exchanger comprises a washing hose connected to a high-pressure washing fluid source and provided with a nozzle at its end. In addition, the apparatus comprises a rotator for rotating the washing hose about its longitudinal axis, and a feed device for pushing the washing hose from below upwards into the heat exchanger tube to be cleaned and for pulling it back down and out of the heat exchanger tube. The nozzle used is preferably provided with holes opening in opposite directions towards the tube walls, so that a high-pressure washing fluid jet is ejected out of the nozzle in substantially all direc- tions.

The apparatus preferably comprises a support- ing device which can be attached to the lower end of the heat exchanger tubes or to some other structure in the lower part of the heat exchanger and which is so arranged that it supports the washing hose and nozzle and guides them into the heat exchanger tube to be cleaned.

The apparatus preferably comprises a rela- tively rigid protective sheath of a certain length placed between the feed device and the supporting de-

vice, the washing hose moving inside said sheath from the feed device to the supporting device. Thus, when the feed device is pushing the washing hose, the hose will not bend or go the wrong way ; instead, guided by the protective sheath, it will advance to the support- ing device, which again will force the washing hose into the desired tube to be cleaned.

The feed device preferably comprises e. g. two freely rotating feed rollers engaging the washing hose from opposite sides. The directions of the rotational axes of the feed rollers can be adjusted in relation to the direction of the rotational axis of the washing hose. The feed device also preferably comprises a con- trol device for the adjustment of the direction of the rotational axes of the feed rollers. Thus, by turning the feed rollers engaging the hose and remaining oth- erwise stationary, they can be caused to move or feed the washing hose in either direction relative to the feed rollers, depending on their deflection angle relative to the hose, as the hose is rotating.

The rotator preferably comprises a rigid tube, to whose first end the washing hose is con- nected. Also connected to the tube is a power means for rotating the tube. Thus, as the tube is being ro- tated by the power means, the washing hose, which is pressure-tightly connected to it, and the nozzle at the other end of the washing hose are also rotated.

Further, the high-pressure washing fluid source is preferably connected to the second end of the tube via a joint rotatable about the longitudinal axis of the tube and provided with a suitable sealing bush.

Thus, the basic idea of the invention can be regarded as consisting in cleaning the heat exchanger tubes using a very high pressure, preferably 100-200 MPa, and with as small an amount of water as possible from the lower ends of the substantially vertical tubes, and additionally using a rotating nozzle. Under

these general terms, the tube to be cleaned remains clean as the small amount of wash water and the impu- rities are immediately removed from the tube when an intensive jet is applied with full power to the layers of dirt to be loosened. In addition, the rotating noz- zle ensures that all parts of the tube wall are thor- oughly washed at the same time, thus leaving no blind spots in the tube. The apparatus and method of the in- vention are very simple and reliable and they can be easily used in all heat exchangers provided with ver- tical heat exchanger tubes accessible from their lower ends.

In the following, the invention will be de- scribed in detail by the aid of an embodiment example with reference to the attached drawings, wherein Fig. 1 presents a diagrammatic view of the apparatus of the invention, Fig. 2 presents a more detailed view of the rotator of the apparatus, and Fig. 3 presents a more detailed view of the feed device of the apparatus.

Fig. 1 presents a diagrammatic view of the apparatus of the invention. The tubular heat exchanger 1 contains vertical heat exchanger tubes 2. At least the lower end of the tubes is open during the cleaning operation. The apparatus comprises a washing hose 3, which can be inserted into the heat exchanger tube 2 and has a nozzle 4 at its end. The washing hose runs via a feed device 5, which pushes the hose into the tube to be cleaned. The hose is supported and guided into the tube to be cleaned by means of a supporting device 8. Between the supporting device 8 and the feed device 5, the hose 3 runs inside a relatively tight protective sheath 9. The washing hose 3 comes into the feed device 5 from a rotator 6, by means of which the washing hose is rotated about its longitudinal axis.

Through the rotator 6, the washing hose 3 is connected

by a connecting hose 17 to a high-pressure washing fluid source 7, the pressure range used being e. g.

100-250 MPa. The connecting hose 17 comprises an ex- tendable portion 18 and the rotator 6 is provided with wheels 19 permitting movement in the direction of the washing hose.

Fig. 2 presents a more detailed view of the structure of the rotator 6. The rotator comprises a rigid tube 13, the second end of the washing hose 3 being pressure-tightly connected to the first end 14 of said tube. Connected to the second end 15 of the tube 13 is a connecting hose 17 with a sealing bush 16 forming a pressure-tight joint, yet permitting rota- tion of the tube 13 while the sealing bush 16 and the connecting hose 17 remain stationary.

Disposed around the tube 13 is a worm gear 20 with a pneumatic power means 12 coupled to it. By means of these, the tube 13 can be rotated in the de- sired direction, so that the washing hose 3 pressure- tightly attached to the tube and the nozzle 4 at its other end are rotated as well.

Fig. 3 presents a more detailed illustration of the structure of the feed device 5. The feed device comprises a guide sleeve 21 for guiding the washing hose into the feed device and a guide cone 22 for guiding the washing hose from the feed device into the protective sheath 9, through which it goes to the sup- porting device 8 and further into the tubes 2 to be cleaned. The feed device 5 comprises a roller frame 23 placed between the guide sleeve 21 and the guide cone 22, with two feed rollers 10 mounted in the roller frame and pressed against the washing hose 3 from both sides as it passes between them, in other words, the washing hose runs between the feed rollers engaging the washing hose from opposite sides.

The feed rollers are swivellably mounted in the roller frame 23 so that they can be turned by a

common control device 11. Thus, the rotational axes of the feed rollers 10 may be parallel to the longitudi- nal direction of the washing hose 3, or alternatively the feed rollers can be turned in either direction, yet so that when the axis of one roller turns in one direction, the axis of the other roller on the other side of the washing hose turns in the opposite direc- tion through a substantially equal angular distance.

Thus, as the washing hose is rotating, the feed roll- ers rotate in contact with the surface of the washing hose. As the rotational axes of the feed rollers have been turned into an oblique angle relative to the lon- gitudinal direction of the washing hose, they move or feed the washing hose in the desired direction at the desired speed, the direction and speed depending on the rotational speed of the washing hose and on the deflection angle of the feed rollers.

The apparatus presented in the drawings works as follows. From the high-pressure washing fluid source 7, a pressure of 100-200 MPa is supplied via the connecting hose 17 into the rotator 6. The rotator rotates the tube 13 and together with it the washing hose 3, which is pressure-tightly connected to it, as well as the nozzle 4 attached to the hose. At the same time, the rotator 6 guides the high-pressure washing fluid into the washing hose 3. As the washing hose 3 is rotating, the longitudinal movement of the washing hose 3 and nozzle 4 is controlled by turning the feed rollers in the feed device 5. By means of the support- ing device 8 mounted at the lower end of the tubular heat exchanger 1, the nozzle 4 and the end of the washing hose are guided into the heat exchanger tube 2 to be cleaned. Thus, the high-pressure fluid jet pro- duced with a small flow of fluid is at first applied to the lower end of the tube 2 to be cleaned and then gradually upwards towards thee upper part of tubular heat exchanger. The rotating nozzle 4, the powerful

hydraulic jet discharged from it and the unobstructed exit flow downward from the tube guarantee that impu- rities are effectively removed from all parts of the interior surface of the tube with maximal injection power. By driving the nozzle 4 in this manner right up to the upper end of the tube 2 at a suitable speed, the tube is made clean, and by then pulling the nozzle back down while still jetting at the same time, a fi- nal check and rinsing are carried out, thus guarantee- ing a very clean washing result. After each tube of the tubular heat exchanger has been treated separately in this manner, the heat exchanger will have heat transfer properties corresponding to those of a new one.

In the foregoing, the invention has been de- scribed by way of example with reference to the at- tached drawing while different embodiments of the in- vention are possible in the scope defined in the claims.