The invention relates to a separation apparatus for sludge, which comprises a screw separator, which has a sieve pipe, a feeding opening for leading in sludge to be separated, a discharge opening for leading out separated sludge and a conveyor screw inside the sieve pipe, a feed pump for pumping sludge to the feeding opening and a control device for adjusting the pumping speed of the feed pump. The invention further relates to a method for adjusting the pumping speed of a feed pump of a separation apparatus. Large amounts of sludge manure are generated on domestic animal farms. Sludge manure is a mixture in liquid form, which contains animal excrements, urine, litter, water and fodder remains. The consistency of the sludge manure can vary from slightly moist to completely fluid. Sludge manure can be utilized for example as a fertilizer and in biogas reactors as a raw material for gas production. In order to make further processing of the sludge manure easier, it is often necessary to separate the solid and liquid material in the sludge manure from each other. The term separation is used for the separating of solid and liquid material and it can be done chemically by precipitation or mechanically with different separation devices. One device commonly used in mechanical separation is a screw separator. Screw sep- arators can, in addition to sludge manure, also be used for separating other kinds of sludges containing solid material and liquid.

The screw separator has a sieve pipe comprising a perforated wall, inside of which there is a conveyor screw rotated with a motor. In the first end of the sieve pipe there is a feeding opening and in the second end a discharge opening. The sludge is pumped with a feed pump via the feeding opening into the sieve pipe, where the rotating conveyor screw pushes the sludge toward the discharge opening. Inside the sieve pipe, liquid is removed from the sludge through holes in the wall, whereby its liquid content is reduced. In the end of the sieve pipe closer to the discharge opening, a "plug" is formed from partially dried sludge mass, which prevents the sludge from flowing in liquid form out through the discharge opening of the sieve pipe. A rise in pressure in the sieve pipe behind the "plug" contributes to the liquid being removed from the sludge through the wall of the sieve pipe. Dried sludge pushing out of the discharge opening of the sieve pipe is a moist paste-like mass. The partially dried sludge mass plug remaining in the sludge advancing in the sieve pipe is important for making possible the continuous unmanned use of the screw separator. A problem with known screw separators is the adjustment of the pumping speed of the feed pump to be optimal. The consistency and solid matter content of sludge generated especially on domestic animal farms, i.e. sludge manure, can vary greatly, which affects the pumping speed of the sludge and the advancing of the sludge in the sieve pipe. The sludge must be pumped at a sufficient speed, so that a planned amount of sludge can be processed. An excessively high pumping speed however raises the pressure of the sludge manure in the sieve pipe, whereby the sludge can advance in the sieve pipe faster than the rotating speed of the conveyor screw. The pressure generated in the sieve pipe can discharge in an explosive man- ner from the discharge end of the sieve pipe, whereby sludge manure spreads widely in the area around the separator. After the discharging, a new sludge mass plug must be formed in the feed material moving in the sieve pipe, so that the use of the separator can be continued.

The pressure of the sludge prevailing in the sieve pipe of the screw separator can be measured with pressure sensors that can be installed inside the sieve pipe. The pressure sensors do however not function reliably in sludge containing dry matter. Publication US 2014/0076801 describes a screw separator, where the operation of the device is adjusted by monitoring the torsion resistance of the conveyor screw. In publication DE 10336215 the advancing speed of the dry feed material in the discharge end is estimated by heating the surface of the feed material with a heater and measuring temperature differences in the feed material at two different distances from the heater. Measuring based on temperature differences is inaccurate, especially in sludge containing dry matter with different heat conductivities.

An object of the invention is to provide a separation apparatus and a method for adjusting the pumping speed of a feed pump in a separation apparatus, with which problems related to prior art can be reduced. The objects according to the invention are achieved with a separation apparatus and method, which are characterized by what is presented in the independent claims. Some advantageous embodiments of the invention are presented in the dependent claims. The separation apparatus for sludge according to the invention comprises a screw separator, which has a sieve pipe, a feeding opening for leading in sludge to be separated, a discharge opening for leading out separated sludge and a conveyor screw inside the sieve pipe. The separation apparatus further comprises a feed pump for pumping sludge to the feeding opening, a control device for adjusting the pumping speed of the feed pump and measuring means for measuring the discharge speed of sludge discharged from the discharge opening. The control device can be set to adjust the pumping speed of the feed pump based on the discharge speed of the sludge.

In an advantageous embodiment of the apparatus according to the invention, said measuring means are outside the sieve pipe in connection with the discharge open- ing. The discharge speed of the sludge is thus measured from sludge which has already pushed out of the sieve pipe. This sludge has already been separated, whereby a large amount of liquid has been removed from it.

In a second advantageous embodiment of the apparatus according to the invention, said measuring means comprise a roller rotating around an axis, arranged in con- nection with the discharge opening, the outer periphery of which roller is arranged in the path of the sludge discharging from the discharge opening. The dry matter content of the sludge processed by the screw separator can be 20-25 weight-%. Such a separated sludge is to its nature a paste-like mass, which is discharged out of the separator as a solid, firm bar. The roller arranged in connection with the dis- charge opening, the outer periphery of which extends to the path of the sludge discharging from the discharge opening, thus rotates substantially with the same speed as the sludge mass pushing out of the discharge opening advances.

In a third advantageous embodiment of the apparatus according to the invention, said measuring means comprise a meter of the rotational speed of the roller. Said meter of the rotational speed is advantageously a pulse sensor.

In still another advantageous embodiment of the apparatus according to the invention, the screw separator further comprises a spatter sensor for detecting sludge discharging from the discharge opening, which is substantially more moist than the dry matter content aimed for. The spatter sensor is advantageously outside the sieve pipe, at a distance from the discharge opening. If the sludge mass plug formed in the discharge opening of the sieve pipe breaks, the pressure required for removing the liquid is not generated inside the feeding pipe. The sludge led into the sieve pipe thus exits through the discharge end of the sieve pipe as a practically unprocessed, running liquid. The spatter sensor is meant to detect such situations, where the screw separator does not function in the intended manner. Sludge in running form spatters as drops in front of the feeding pipe at quite a long distance from the discharge opening, so the spatter sensor can be placed at a distance of for example 100-200 mm from the end of the discharge opening. The spatter sensor can be a humidity sensor. Unprocessed sludge usually exits through the discharge opening as a liquid spray at high pressure, so the spatter sensor can also be a mechanical sensor which reacts to a force directed onto it.

In still another advantageous embodiment of the apparatus according to the invention, the feed pump is arranged at a distance from the screw separator and con- nected to the feeding opening with a pipe. The feed pump and screw separator can thus be apart from each other and situated in the same building in different parts or even in different buildings.

In the method according to the invention for adjusting the pumping speed of a feed pump of a separation apparatus, an upper limit is set for the discharge speed of the sludge discharging from the discharge opening. In the method, the discharge speed of the sludge discharging from the discharge opening is measured and the measured discharge speed is compared to the upper limit for the discharge speed. If the measured discharge speed exceeds the upper limit, the pumping speed of the feed is reduced. A rise in the discharge speed of the sludge is a sign that the pressure inside the sieve pipe has risen too high, whereby the risk for an explosive discharging of sludge through the discharge opening rises. By reducing the pumping speed of the feed pump, the pressure in the sieve pipe can be made to drop to a safe level.

In an advantageous embodiment of the method according to the invention a lower limit is additionally set for the discharge speed of the sludge discharging from the discharge opening, and the measured discharge speed is compared to the lower limit for the discharge speed. If the measured discharge speed is below the lower limit, the pumping speed of the feed pump is increased. By reacting to the discharge speed falling below the lower limit it is ensured that a sufficient sludge processing capacity is achieved with the separation apparatus. In a second advantageous embodiment of the method according to the invention, the discharge speed is measured from the sludge which has discharged from the discharge opening. The measuring is thus done outside the sieve pipe of the screw separator.

In a third advantageous embodiment of the method according to the invention, a lower limit is set for the dry matter content of the sludge discharged from the discharge opening, the dry matter content of the sludge discharging from the discharge opening is estimated, and the feed pump is stopped if the estimated dry matter content falls below the lower limit for the dry matter content. Typically, the dry matter content of the sludges led into the screw separator can be below 10 weight- and the dry matter content of the sludge exiting the separator can be 20-25 weight-%. The set lower limit for the dry matter content is naturally higher than the dry matter content of the sludge led into the separator. A low dry matter content of the sludge discharged from the discharge opening is a sign that the screw separator is not operating in the intended manner, whereby the conveyor screw should be stopped in order to check the operation of the device. The dry matter content can be estimated indirectly based on the behaviour of the sludge discharging from the discharge opening, such as its flowability and spattering.

An advantage of the invention is that the measuring means on the outside of the screw separator's sieve pipe are easy to service.

An advantage of the invention is further that no pressure or hard mechanical strain is directed at the measuring means, whereby they do not easily break.

Still another advantage of the invention is that adjustment of the pumping speed based in the discharge speed of the processed sludge is simple to achieve and reliable.

In the following, the invention will be described in detail. In the description, reference is made to the enclosed drawings, in which figure 1 shows as an example a separation apparatus according to the invention seen from the side. Figure 1 shows as an example a screw separator 6 of a separation apparatus according to the invention as seen from the side. The screw separator has a support frame 8, on which the sieve pipe 10 in the horizontal position in the figure is supported. The sieve pipe is shown in the figure as cut through in the longitudinal direction in order to better bring out the structure of the screw separator. Inside the sieve pipe there is a conveyor screw 12, which extends from the first end of the sieve pipe to the second end of the sieve pipe. The conveyor screw has an axis 13, which is rotated with a motor 18 in the second end of the sieve pipe. In the wall of the sieve pipe, close to the first end of the sieve pipe, there is a pipe-like feeding opening 14 penetrating the wall, through which sludge to be separated is led into the sieve pipe. In the second end of the sieve pipe there is an end plate, which has a discharge pipe 28. At the end of the discharge pipe there is a discharge opening 16. On the inner surface of the wall of the sieve pipe there are flow channels 36 circulating the inner surface, which are covered with a close-meshed, liquid-permeable net 34. The flow channels are connected to an outlet pipe 32 leading through the wall of the sieve pipe. The separation apparatus further comprises a feed pump 20, which is connected with a pipe 21 to the feeding opening. The operation of the feed pump is controlled with a control device 26. The sludge to be separated is pumped with the feed pump along the pipe 21 inside the sieve pipe 10 of the screw separator. In the second end of the sieve pipe of the screw separator according to the invention, outside the edge pipe, there is a roller 22. The roller is supported by means of a shaft 38 above the discharge pipe, so that the cogged outer periphery of the roller cuts the path of the sludge mass discharging from the discharge opening. The shaft is supported by its first end with a pivot pin to lugs 44 in the end plate of the sieve pipe. In the second end of the shaft there is an axis 42, around which the roller is mounted on bearings to rotate. In figure 1 the dotted line shows a separated sludge mass bar 40 discharging from the discharge opening. The outer periphery of the roller settles in contact with the outer surface of the sludge mass bar, whereby the roller starts to rotate around the axis 42. The shaft 38 has a pulse sensor 46, which measures the rotational speed of the roller. The pulse sensor is connected with a wired or wireless data transfer connection to the control device 26 of the sludge pump. The roller 22, the support means of the rollers and the pulse sensor 26 together form the measuring means for measuring the discharge speed of the sludge pushing out of the discharge opening. Close to the second end of the sieve pipe 10, at a distance from the discharge opening 14, there is further a spatter sensor 24, which is in the same way as the pulse sensor connected with a wired or wireless data transfer connection to the control device 26. The spatter sensor is placed so in relation to the discharge opening that part of the liquid discharging from the discharge opening at a high pressure hits the spatter sensor, i.e. the spatter sensor is in the advancing path of the discharging liquid. The spatter sensor detects liquid hitting or accumulating on its surface and sends information thereof to the control device.

The screw separator is used for separating sludge consisting of liquid and dry matter mixed therein. During separation, liquid is separated from the sludge, whereby the dry matter content of the sludge increases. The sludge to be separated can for example be sludge manure generated on domestic animal farms, which includes water, animal urine and excrement, fodder remains and litter. The sludge can include other organic substances or mixtures mixed into the sludge manure, such as food industry by-products. The sludge is pumped with a feed pump via the feeding open- ing into the sieve pipe and the conveyor screw rotated by the motor pushes the sludge in the sieve pipe toward the discharge pipe 28. While moving along the sieve pipe, part of the liquid in the sludge flows through the net 34 into the flow channel 36 and leaves the sieve pipe along the discharge pipe 32. As the liquid is removed, the dry matter content of the sludge increases. The separated sludge exits the sieve pipe 10 through the discharge opening 16 of the discharge pipe 28. The separated sludge exiting through the discharge opening is typically a paste-like mass, the dry matter content of which is 20-25 weight-%.

In the method according to the invention the sludge separation apparatus is used so that an upper limit is set for the discharge speed for the separated sludge discharging from the discharge opening. The upper limit is determined in an experi- mental manner, so that at lower speeds than the discharge speed, the pressure of the sludge in the sieve pipe does not rise too high. The pressure of the sludge in the sieve pipe is advantageously below 1 bar. The discharge speed can thus for example be 0.4-0.8 meters per minute, advantageously 0.5-0.7 meters per minute. The discharge speed of the sludge discharging from the discharge opening is measured continuously or at suitable intervals, and the measured speeds are transmitted to the automatic control device 26 of the feed pump 20. The control program of the control device compares the measured discharge speed to the set upper limit of the discharge speed. If the measured discharge speed exceeds the upper limit, the control device decreases the pumping speed of the feed pump. Thus it is ensured that the pressure of the sludge in the sieve pipe cannot rise too high.

In the method, a lower limit can also be set for the discharge speed of the sludge discharging from the discharge opening and the measured discharge speed can be compared to the lower limit for the discharge speed. If the measured discharge speed is below the lower limit, the pumping speed of the feed pump is increased. In the method the discharge speed is measured from the sludge which has discharged from the discharge opening, i.e. from the sludge, which has already left the sieve pipe and the discharge pipe continuing from it.

In the method according to the invention, a lower limit can additionally be set for the dry matter content in the sludge discharging from the discharge opening, and the dry matter content of the sludge discharging from the discharge opening can be estimated. The estimation can be done indirectly, based on the properties of the sludge discharging from the discharge opening. If the sludge discharging from the discharge opening is a liquid, running solution, its dry matter content is too small, i.e. it falls below the set lower limit. A running, liquid state of the discharging sludge is a sign that the slightly dried, paste-like sludge mass, which forms in the sieve pipe in a normal use situation, has for some reason left the sieve pipe. A high enough pressure does thus not form inside the sieve pipe, which pressure would force the liquid through the net 34 and along the outlet pipe 32 out of the sieve pipe. The sludge led into the sieve pipe thus exits through the discharge opening 16 as a practically unseparated, uncontrolled liquid spray, which is detected with the spatter sensor 24. The information detected by the spatter sensor is transmitted to the control device, which stops the feed pump and alerts the personnel using the separation apparatus.

Some advantageous embodiments of the sludge separation apparatus and method according to the invention have been described above. The invention is not limited to the solutions described above, but the inventive idea can be applied in different ways within the scope of the claims.