SE509082C2 - Electrostatic separator for purifying flue gases - Google Patents

Abstract

A purification apparatus for removing substances from gases has the gas mixed with water and then supplied at a tangent into a chamber created by a gap between an external wall (3) and an internal conical wall (13). From here the gas passes between electrodes (15-17) that charge the substances and then into a channel with a smaller diameter than the external wall. Charged particles are captured by a film of water formed over the length of the external wall and the inside of the small channel.

Description

509 082 From Fig. 3. it can be seen that the degree of purification of the electricity must be approximately 90% in order to be able to reach the emission limit of 25 mg / nm3 dry gas. - From Fig. 2. it can be seen that the total necessary collector area should be approximately 28 m2 if we assume that the secondary collectors are as efficient as the primary collectors in dry electricity. This assumption is realistic and on the cautious side because the particles in dry endastlter are only affected by the gravity of smooth collectors while the gas in a filler body bed is forced to change direction again and again and the particles that want p. G.a. its weight continue straight fi- am easier to hit a wet surface. The surface area of different primary collectors varies between 50 and 95 m2 / m3 collector volume, which is why the need for space for the secondary collector is small.

From Fig. 4. it can be seen that the electricity demand of the electricity is only about 120 watts / 1 MW panel.

The requirement of 25 mg / nmß dry gas is very mild, which is why the electricity is small and the electricity consumption is low. If, on the other hand, the requirement had been set at 5 mg / nrn3 dry gas, about 80 m2 / l MW boiler total collection area would have been needed and the electricity demand would have risen from 120 watts to 810 watts / l MW boiler ect.

Construction and function: The construction of the device according to the invention is shown in Figs. 5 and 6.

The flue gases are led through a tangential inlet 02 into a cylindrical container 03. At the inlet, water is poured into the gas stream, so that the dry temperature of the gases is lowered, the gases become saturated with water vapor and excess water is supplied in liquid form. The gases rotate in the space between the outer jacket and an inner wall 13. Due to the rotation, the liquid water is thrown on the inner wall of the jacket 03 which is grounded and the water forms a water m lm The gases continue downwards through the gap between 03 and 13. Under 13 hangs in a support 14 a device with emission electrodes. The support 14 is electrically insulated from the outer casing with the insulator 12 and connected to a voltage supply which supplies the emission electrodes with high voltage up to the order of 40-60 kV. The emission electrodes consist of a ring 15, of a number of rods 16 and a ring 17. The electrodes have pointed spikes which send a so-called Corona field to the nearest earthed surface which is 03 and which thus functions as a primary collector. - The dust particles become charged by the field and begin to migrate towards the water men lmen on the mantle surface.

In addition, the particles are affected because the gas rotates by centrifugal forces which also drive them towards the water.

When the liquid has passed the emission electrodes, it and the gases are directed with a cone 18 towards a smaller diameter where there is a scaling ring 24 which peels off the water from the periphery and leads it out via line 19. The solid particles stuck in the primary collector are purified from the system already in this step.

. . . In the next step, the gas continues downwards and threads the inner wall of an annular bed 09 of filling bodies. The inner and outer diameters of the bed are chosen so that the radial velocity of the gas into the bed is of the order of 2 - 4 rn / s and the velocity out of the order of I - 2 rn / s. Due to the fact that the gas mass rotates when it enters the bed, the actual gas velocity on the inner surface is much greater, which is advantageous because the particles then do not have as easy as at low speeds to follow the gas when it is angled in different directions around the filling bodies. The. ° radial velocity through the bed, you want to be high enough in the beginning to get good purification without km 509 082 too great pressure drop. The outlet speed must be low so that small drops of pride can not follow. Since the bed is annular, the outlet speed automatically becomes significantly lower than the inlet speed. As extra security, a drip separator 10 according to the prior art can be installed as the outer layer of the ring.

The bed is irrigated via gutters 07. The innermost gutter also releases water into the center channel, the other gutters to the top of the bed. The water fl fate is low or nothing in the outermost channel and gets higher and higher the closer you get to the center.

The dirty water 11 from the bed collects at the bottom of the device and is led through line 25 for purification.

A washing device 04 is installed, which removes the emission electrodes and can be supplied via pipe 05 with washing water if the electrodes or after a certain period of operation have become dirty. During the washing period, the electricity to the electrodes is switched off.

A washing device 08 cleans the inner surface of the filling body bath via pipe 22 if it has become so dirty that the normal water pouring is no longer sufficient.

The surface seams for the upper part of the plant are the same even if the treatment requirement varies within wide limits. For stricter requirements, a sharply rising electrical element according to Fig. 3 is required. A larger number of electrode rods 16 is therefore hung between the rings 15 and 17. Since the rods are placed on a large radius, there is sufficient space for a large number of rods to increase the electrical power. A more powerful power supply is also needed. The size of the full body bath must also be adapted to the requirement.

A solution for the water purification is shown in Fig. 6.

The water from the secondary collector is pumped by pump 28 to a tank 27 approximately at half the height of the tank. The sediment drops to the bottom of the tank and the cleaner water rises towards the top of the tank from where it is led through line 06 to the gutters 07. The water level in the reservoir 11 is kept constant by draining any excess water to a container 23 as a replacement for the water evaporated to saturate the gas with water vapor. and by refilling water from either, for example, an electric condenser or from a water pipe.

The water from the primary collector is first collected in a container 23 to which refill water is also supplied from the reservoir 1 l so that the water level is kept constant. The water is then pumped with pump 29 to the inside of a casing 26 which is found in the tank 27 approximately at half the height of the tank. Cleaner water is then led from the top of the screen jacket via line 01 to the gas inlet 02. 509 082 To increase the collector surface of the annular bed 9 without simultaneously increasing the pressure drop, two or fl your types of filling bodies can be used. Closest to the center are bodies with large outer dimensions, which most often means large cavity, low surface area / volume and low relative pressure drop (= pressure drop at a certain speed compared with other bodies at the same speed). The gas velocity is greatest near the center, which is why the largest bodies with a low pressure drop are placed there. Further out in the periphery, the speed is low, which is why you can insert small bodies with a large area / volume. At the far end you can put even smaller bodies with even larger area / volume. As an example of choosing two sizes, the furthest 3.5 ”bodies with 44 m2 surface / m3 are inserted where incoming speed = 4 m / s and outgoing speed 2 m / s and furthest 1” bodies with 225 m2 surface / m3 with incoming speed = 2 rn / s and outgoing speed lm / s. The advantage of varying body size is also that closer to the center where the gas contains the most mare fi the clogging risk with large bodies is significantly less than with small bodies while further out in the periphery the gas content is lower so the clogging risk for small bodies is also less there.

The function of the electricity has been described with flue gases from a solid fuel package as an example. The filter is not limited to this use but is intended for filtering all types of stubble from different sources.

Claims (1)

Device for purifying gases from dust, characterized in that the gas is mixed with water and is conducted tangentially in a chamber between the outer wall 03 and an inner conical wall 13 and thence through a gap between the outer wall and the inner wall past electrodes which charge in the sto fl particles and then inwards to a channel smaller in diameter than the outer wall and that the particles are trapped in a water fi lm formed along the outer wall and the inside of the smaller channel. Device according to claim 1, characterized in that a scaling ring 24 placed in the outer wall of the smaller channel peels away the water ellipse and the bound mare from the wall. Device according to Claim 1 or 2, characterized in that the gas is led out of the device through a water-filled bed of filling bodies.