WO2011006853A1

WO2011006853A1 - Exchangeable nozzle device for pressure relief of materials containing erosive compounds

Info

Publication number: WO2011006853A1
Application number: PCT/EP2010/059951
Authority: WO
Inventors: Pål Jahre NILSEN; Bjarne Fikse; Per LANGØY; Johnny KÅRBØ
Original assignee: Cambi As
Priority date: 2009-07-13
Filing date: 2010-07-12
Publication date: 2011-01-20
Also published as: NO20092646A1; NO331912B1

Abstract

Exchangeable nozzle device for relief of pressure in a mixture of steam and erosive materials, encompassing a pipe (2) and a flange (3) for fastening onto a pressure release tank. The pipe (2) is fitted with a constriction (4) and a deflection plate (5), where the constriction (4) and the deflection plate (5) are manufactured from a material with a high resistance to erosion, preferably a ceramic such as, for example, SiNi, AIOx, WC, or the like.

Description

Exchangeable nozzle device for pressure relief of materials containing erosive compounds

The present invention relates to an exchangeable nozzle device for relieving the pressure in a mixture of steam and erosive materials, encompassing a pipe with a flange for fastening onto a pressure relief tank.

A nozzle device for the supply of a fuel or a coke slurry to a reactor is known from US 4,268,017. The device comprises an outer nozzle casing with a co-axially feeding nozzle that can be pulled out, which is surrounded by fireproof, ceramic fibres, said feeding nozzle is fastened to the casing with the help of flanges at the outer end of the casing and the feeding nozzle. This publication describes that previous, known solutions have been subjected to erosion and that the replacing of nozzles has led to extended periods with breaks in operation. The aim of the solution according to this publication is to be able to provide an exchangeable nozzle for a reactor.

In present plants for thermal hydrolysis of organic sludge, the organic sludge is heated to 150-170 ⁰C in a pressurised reactor and brought further after a certain time to an approximately non-pressurised, pressure release tank, a so- called flash tank. The pressure relief will cause a phase transition in the water which will expand and tear apart the cells and other physical structures of the water. This results in a desired improvement of the characteristics of the sludge with regard to reduced viscosity, and bioavailability. The sludge mixture that is fed into the flash tank from a reactor at high pressure will be accelerated to a great velocity in the pipe between the reactor and the flash tank and at the inlet of the flash tank. The eroding particles in the sludge mixture will thereby lead to erosion. To reduce the erosion in the pipes between the reactor and the flash tank one has previously used bends with a large radius. In the flash tank it has, in addition, been common to install wear-plates where the inlet spray hits the wall tangentially in the flash tank. The valve that opens for the sludge from the reactor must be located as near to the reactor as possible to prevent that stagnant sludge in the possible pipe between the valve and the reactor does not reach the necessary hydrolysis temperature (ca 165 ⁰C) and thereby does not meet the hygiene requirements. An arrangement of this type is known from EP 0784504.

To further reduce the wear and also control the return of steam, one has inserted area restrictions on the flow cross-section in the valve. This creates local high speeds that can lead to erosion in downstream pipes, that is, in the pipe or pipes between the reactor and the flash tank.

A method for continuous hydrolysis of organic matter is known from the publication EP 1198424, where all the pressure from the reactors is relieved to the flash tank. EP 1198424 describes the given limitations of the process for treatment of biomass with a high content of erosive material.

Both the two mentioned publications describe pressure relief and transfer of steam and organic matter to the flash tank, where the valve that controls the transfer of steam and organic sludge is placed in the pipe between the reactor and the flash tank.

A nozzle with a built-in deflection plate for use as by coating is known from EP 1396286.

WO 9613562 describes a nozzle for processing of hydrocarbons where a nozzle constructed with a deflector is used. US 5,813,087 describes a spray nozzle for cleaning, where a deflector is used to deflect the spray.

Further publications that describe pressure relief of this type are, for example, WO 98/55408, WO 2008/115777 and WO 03/043939.

New calculations and measurements that have been carried out show that the flow rate can be limited by the speed of sound in the steam/sludge mixture at a location in the pipe between the reactor and the flash tank, instead of the reduced area of the valve. This can imply that the flow rate is unknown and that the time to empty the reactor can not be determined. Therefore, it is desirable to be able to define flow rates and emptying times in a more reliable way.

A fastest possible pressure relief and thus the fastest possible steam explosion/volume expansion will result in the largest mechanical degradation of the organic matter and thus the largest possible yield for later production of, for example, biogas. This will also mean that eroding particles will not be accelerated to a high velocity before the outlet of the blow pipe and that problems of wear in the pipe transition(s) between the reactor(s) and the flash tank are thereby substantially reduced.

Such acceleration and pressure relief in a small, controlled area and a reduced speed in the pipe connection(s) between the reactor(s) and the flash tank can be reached by arranging for an area restriction at the end of the blow pipe from the reactor(s), inside the flash tank. This is also mentioned in EP 1198424, but this publication neither describe, nor suggest how this can be achieved in practice. This publication describes at the same time that the drop in pressure is distributed between a control valve in the pipe and nozzle placed towards the end of the pipe and mentions in particular that the amount of eroding particles must be low.

The area restrictions can be shaped as a nozzle from materials with large resistance to wear, for example, ceramics. The geometrical shape of the nozzle, and also the placing and shape of the blow pipe, make it possible to guide the spray towards the liquid surface in the flash tank and thereby prevent wear of the tank wall.

A vital advantage of the present invention is that one achieves a quick steam explosion and thus a more comprehensive rupture of cells and other physical structures and also a short time for particle acceleration towards a deflection plate. The latter means an effective crushing of cells and other, relatively large particles and relatively small problems with wear caused by the smaller eroding particles. Another advantage of the invention is that the problems of wear and erosion in the pipe between the reactor and the flash tank and also in the blow valve are avoided or reduced to a considerable extent. This implies that one can use ordinary bends with a standard radius and wall thickness in pipes between the reactor and the flash tank.

A further advantage of the present invention is that the nozzle device can be fitted/replaced from the outside of the flash tank so that one does not have to dismantle the flash tank for the fitting/replacing of the nozzle device. Thus, one does not have to maintain possible wear plates in the tank.

The nozzle device according to the present invention makes it possible to calculate the flow rate from the reactor to the flash tank more accurately, as the critical cross section in the nozzle device and the pressure conditions in the nozzle device are known. Furthermore, the nozzle device has a simple geometry, which means that sophisticated materials with a high resistance to erosion, such as ceramics, can be used in parts of the nozzle device.

These advantages are achieved with an Exchangeable nozzle device for relief of pressure in a mixture of steam and erosive materials, encompassing a pipe with a flange for fastening to a pressure relief tank that is characterised in that the pipe is fitted with a constriction and a deflection plate, where the constriction and the deflection plate are made from a material with a large resistance to erosion, preferably a ceramic such as, for example, SiNi, AIOx, WC or the like.

According to one embodiment, the constriction and the deflection plate are manufactured in one integrated unit. With regard to an alternative embodiment the constriction and the deflection plate are manufactured as two independent parts.

The constriction and the deflection plate are preferably fixed in the pipe so that they can be interchanged. The constriction has preferably a diameter which is 30-70 % of the inner diameter of the pipe. The invention will now be explained in more detail with the help of the non- limiting embodiment examples with reference to the enclosed figures, where:

Figs. 1 a and 1 b show a section of two embodiments of a nozzle device with regard to the present invention.

Fig. 2 shows a partially cut through flash tank and shows alternative locations of the nozzle devices shown in fig. 1.

Fig. 3 is a diagram that shows pressure, speed of sound and flow velocities in a sludge/steam mixture in a pipe between the reactor and the flash tank in a known system.

Fig. 4 is a diagram that shows pressure, speed of sound and flow velocities in a sludge/steam mixture in a pipe between the reactor and the flash tank in a system that uses a nozzle device according to the present invention.

Figures 1a andi b show a section of a nozzle device according to two embodiment examples of the nozzle device according to the present invention. The nozzle device, generally denoted as 1 , comprises a pipe 2 with a flange 3 at its one end, a constriction 4 and a deflection plate 5 at the other end. In the embodiment shown in fig. 1 a, the constriction 4 and the deflection plate 5 are manufactured as an integrated unit, while in the embodiment in figure 1 b the constriction 4 and the deflection plate 5 are formed as two separate units. The constriction 4 and the deflection plate 5 are manufactured from a material with a high resistance to erosion. The constriction 4 and the deflection plate 5 can be formed so that they can be replaced, such that in the embodiment according to figure 1 a it is possible to interchange the whole integrated unit, while in the embodiment according to figure 1 b it is possible to interchange the constriction 4 and/or the deflection plate 5 according to need.

Yet another advantage with the embodiment according to fig. 1 b is that biological particles (cell matter) with a low density and relatively large diameter are accelerated fast in the constriction of the nozzle and are crushed against the deflection plate 5. Eroded particles with a relatively small diameter and greater density are accelerated slower and do not reach the same velocities at the deflection plate.

The nozzle device 1 shall be placed in an outer wall of a flash tank, where the outer wall of the flash tank is fitted with a pipe of an inner diameter which is approximately equal to the outer diameter of the pipe 2. Furthermore, a flange that shall work with the flange 3 of the nozzle device is placed around the free end of the end of the pipe so that these flanges can be fastened to each other. This solution makes it possible to loosen the connections with the flange 3 of the nozzle device and the flange on the flash tank so that the whole of the nozzle device can be pulled out of the flash tank for maintenance or replacement when necessary.

A constriction 4 is placed near the outer end of the pipe 2 which leads to an increase of the flow velocity. After the flow of liquid with increased velocity has come through the constriction, it hits a contact surface which has a deflection plate 5 that has an inclining wall which means that the direction of flow for the fluid flow changes approximately 90° in relation to the direction of flow in the pipe 2. At the same time, particulate, degradable material in the liquid flow will be broken up. A short constriction results in a pressure relief over a short time, which results in a fast/intense steam explosion which effectively tears up the particulate material. Both the constriction 3 and the contact surface 4 are manufactured from very erosion resistant materials, especially preferred is a ceramic material such as, for example, Si₃Ni₄, AI₂O₃, W₂C, etc.

The shape and assembly of the different components of the nozzle take into consideration the different thermal expansion coefficients for steel and ceramics. Steel has a thermal expansion coefficient that is of the order of five times greater than the coefficient for ceramics. This means that it is

advantageous to use a ceramic material which is pre-stressed at low temperature to ensure the fixing at high operating temperatures also.

Fig. 2 shows a partially cut through flash tank with several possible positions for the nozzle device 1. The flash tank can be fitted with one or more nozzle devices. If there are several nozzle devices fitted in a flash tank, these must be formed such that the sprays from the nozzle device do not hit other nozzle devices and erode these. This can be carried out by varying the length of the pipe 2 and the angle of the deflection plate 5. The shape of the nozzle devices 1 is determining to achieve sufficient tearing up of particulate matter in the liquid stream. Furthermore, it is important to place the nozzle devices 1 so that the outflowing stream of liquid from the nozzle device hits the surface of the liquid that is in the flash tank already so that no erosion of the inner surfaces of the flash tank occurs.

Fig. 3 shows an example of flow velocities and pressure in a pipe between the reactor and the flash tank without the nozzle device according to the present invention. The X-axis is an expression for the length of the pipe between the outlet of the reactor and the inlet of the flash tank. The left part of the X-axis represents the values at the outlet of the reactor, while the right part of the X-axis shows the values at the outlet of the pipe into the flash tank. The pressure curve (P(bara)) shows that the pressure is reduced approximately linearly over the whole distance and finally reaches the same pressure that is in the flash tank and that the liquid stream reaches the speed of sound c_m at an unspecified position in the pipe. The speed of sound results in a limitation for the flow velocity in the pipe and it is important to be able to determine the position and pressure conditions at the critical cross section.

Fig 4 shows an example of flow velocities and pressure in a pipe between the reactor and the flash tank with a nozzle device according to the present invention. The axes in this diagram correspond to the axes in fig. 3. This diagram shows that the pressure sinks markedly less over the pipe length compared to the case shown in fig. 3. The pressure is suddenly considerably reduced as the liquid flows out of the nozzle device according to the invention. The flow velocity increases moderately up to the nozzle, whereupon the velocity increases markedly as the liquid stream comes out of the nozzle. In this case the critical cross section (choked flow) is decided in the nozzle and the flow rate is thereby better defined.

If one assumes that the breakdown of particles in the liquid stream occurs at a powerful pressure change (steam explosion) and that the erosion in the pipe and valves is a function of the flow velocity of the eroding particles, a person skilled in the arts will clearly see that the particle breakdown is much greater in fig. 4 than in fig. 3 because of the much more rapid drop in pressure in fig. 4 and that the erosion is much lower in fig. 4 than in fig. 3 because of the flow velocities. From this follows that with the help of the nozzle devices according to the present invention it is possible to achieve the aims of the invention, namely reduced erosion and improved particle breakdown.

Claims

C L A I M S

1.

Exchangeable nozzle device for relief of pressure in a mixture of steam and erosive materials, encompassing a pipe (2) and a flange (3) for fastening onto a pressure release tank ,

characterised in that the pipe (2) is fitted with a constriction (4) and a deflection plate (5), where the constriction (4) and the deflection plate (5) are manufactured from a material with a high resistance to erosion, preferably a ceramic such as, for example, SiNi, AIOx, WC, or the like.

2.

Nozzle device according to claim 1 ,

characterised in that the constriction (4) and the deflection plate (5) are manufactured as one integrated unit .

3.

Nozzle device according to claim 1 ,

characterised in that the constriction (4) and the deflection plate (5) are manufactured as two independent parts.

4.

Nozzle device according to any of the preceding claims,

characterised in that the constriction (4) and the deflection plate (5) are fastened to the pipe (2) so that they can be replaced.

5.

Nozzle device according to any of the preceding claims,

characterised in that the constriction (4) has a diameter which is 30-70 % of the inner diameter of the pipe (2).