The present invention relates to the controlled delivery of slurries into process equipment such as reactors through which a process material flows while undergoing a chemical or physical change. The invention is concerned with both an apparatus for the delivery of a slurry and a process in which a slurry can be delivered into a reactor under conditions whereby the slurry is delivered in a controlled manner over a period of time at a predetermined rate and a predetermined concentration. The invention is particularly useful in the delivery of slurries into reactors in which a process material flows continuously in order to provide a desired ratio of slurry and/or the solid contained therein to process material over an extended period of time.

One particular use of the invention is in the delivery of catalyst slurries into reactors such as polymerisation or hydrogenation reactors where the process material is a polymerisable material or a mixture of a material to be hydrogenated and hydrogen.

It has been proposed to continuously introduce slurries into process equipment through supply lines from stirred slurry storage tanks. However, in practice this has not been accurately accomplished over extended periods of time due to the settling of solids from the slurry in supply lines and entry ports into the process equipment leading to blockages and system failure and/or undesirable variation in the content of the slurry or its delivery into the process equipment. These problems in turn impair the homogeneity of the reaction to be performed in the process equipment, The present invention addresses those issues.

The present invention provides a method and apparatus for continuous controlled delivery of slurries into process equipment. Process equipment refers to systems in which a physical or chemical change of a process material occurs usually requiring a particular residence time of the process material within the process equipment. The process material may be a liquid containing particulate solids and may also include a gas and the process performed in the process equipment can include mixing, separation, crystallisation or chemical reaction. The process equipment may be a continuous: chemical reactor, bio reactor, separator, mixer, crystalliser or one that performs other unit operations and the reaction is one where a defined residence time within the process equipment is required. The term slurry refers to free flowing liquids containing particulate solids. Gas may be present as a third component. Controlled delivery means that volumetric flow rate and also the ratio of solids to liquids delivered into the process equipment are maintained within specified limits. The volumetric flow rate is determined by the volumetric capacity of the process equipment divided by residence time. The residence time requirements in the equipment differentiate this system from slurry transfer systems where residence time is not defined and slurry can be transferred at high volumetric flow rates in large diameter channels.

The system provided by this invention is one which is sealed between the slurry feed line and the discharge line from the process equipment and although it can operate below ambient pressure it typically operates above ambient temperature.

The slurry delivery system of this invention can be used for solids which are neutrally buoyant but is primarily used with slurries containing solids which float or sink. Although not limited to such an embodiment we will describe the invention in relation to solids which sink and the direction of flow of the solids in unmixed zones is down. The same principles can be used for solids which float but in such cases the direction of flow in unmixed zones is up. The term a line as used herein refers to a pipe or channel used to contain the flowing slurry.

In this invention a slurry is held in a feed tank and passes into the process equipment under controlled transfer. In previous systems problems occur if solids settle on surfaces or bridge across the face of lines or equipment. Settling can be prevented with active or passive mixing. Bridging can be prevented by using lines with diameters which are greater than 10X the diameter of the solids in the slurry and more preferably 20X greater. Although adequate line sizing is important, it can result in velocities which are insufficient to transport solids in unmixed zones other than with gravity assistance.

The present invention therefore provides a device for the delivery of a slurry from a slurry line into process equipment comprising a feed channel between the slurry line and the process equipment wherein the aperture from the slurry line into the feed channel has a maximum dimension of 10 mm and the length of the feed channel is not greater than the maximum dimension of the aperture.

The ratio of solids to liquid entering the feed channel must also be controlled to the level required in the process equipment and is typically controlled by the ratio in a slurry feed tank. The device of the invention is preferably provided in a slurry line which is part of a continuous slurry recycle system comprising a stirred slurry tank and a recycle line from which the slurry is delivered to the process equipment via the device of the invention. In this way the concentration of the slurry can be maintained by monitoring and if necessary adjusting the concentration of the slurry in the slurry tank and the amount of slurry delivered into the process equipment can be controlled by the flow rate of the slurry diverted from the recycle system.

We have found that providing a device having the dimensions specified is used for the delivery of the slurry into the process equipment, deposits of solids and blocking or restriction of lines and delivery locations can be reduced or eliminated within the specified dimensions the preferred dimensions may depend upon the nature of the slurry including both the concentration and the particle size of the solids within the slurry. In a preferred slurry delivery system the device according to the invention can be replaceable to enable the system to operate effectively with slurries of different concentrations and/or containing particles of different sizes and/or travelling at different speeds within the supply line. In a preferred embodiment the aperture of the device of the present invention is circular and the maximum dimension is the diameter of the circle. It is also preferred that the surface of the aperture is smooth and highly polished to remove any irregularities that might provide locations for deposition of particles from the slurry.

The present invention is illustrated by reference to the accompanying Figures in which

Figure 1 shows a slurry delivery system for delivery of slurry to process equipment according to the invention.

Figure 2 shows a slurry delivery device of the invention.

Figure 3 is a section through the delivery device of Figure 2.

Figure 4 shows an alternate slurry delivery device provided with a gas bleed. In Figure 1 slurry is held in a feed tank (1 ) where it is stirred to maintain a uniform distribution of solids within the liquids. The slurry flows through a recycle line (2) using a pump (3) and returns to the feed tank (1 ). The internal diameter of the recycle line is large enough to prevent bridging and the slurry is pumped at a velocity sufficient to transport the slurry. The slurry delivery device (4) diverts a fraction of the slurry from the recycle line (2) to the feed line (5) and into the process equipment (6) and is located above the reactor at minimum distance. The feed line (5) is positioned at 30° or less from the vertical and is preferably vertical. The process equipment (6) is horizontal in this example and can employ active or passive mixing to keep the solids suspended and moving with the process material. Other types of process equipment in different orientations may be used. The discharge line from the process equipment is oriented at 30° or less from the vertical and is preferably vertical. Slurry residue passes to a solids collection vessel (7) below the process equipment. The solids collection vessel separates solids by filtration, gravity or other means. Solids free liquid passes to the liquid discharge line (8) which may employ a flow control system as shown here (9) which includes a flow measuring element with a control valve. Other flow control methods may be used. The discharge line (8) passes to a fluid tank (10) and passes at an elevation above the reactor to keep the system liquid filled. An anti-syphon device (not shown) may also be used.

Figure 1 shows a slurry delivery device (4) of the invention located in a recycle line which is the preferred arrangement. Alternatively the recycle line may be a point in the slurry storage tank adjacent to the slurry dosing device (4) and slurry is recycled within the tank by the stirrer.

The arrangement in figure 1 employs transfer lines and equipment with diameters large enough to prevent bridging. Solids are kept suspended by active or passive mixing where possible. In slow moving unmixed zones, the lines are oriented so that slurry flow is gravity assisted.

If the slurry delivery element (4) is located in the slurry feed tank, flow into the feed line (5) can be promoted by operating the feed tank at elevated pressure or by using a pump on the solids free discharge line (8). A recycle line as shown in figure 1 is preferred. A pump located before the slurry delivery element (4) creates elevated pressure in the recycle line between the slurry delivery element and the return line to the feed tank (1 ). This causes fluid to pass into the feed line (5). If required line restrictors or valves may be used in the recycle return line downstream of the slurry delivery element to increase the back pressure. The liquid to solids ratio within the feed line (5) is the same as the feed tank (1 ) as controlled by the slurry delivery device (4). This may be located within the feed tank but locating it in a recycle line is preferred.

Figure 2 shows the slurry delivery device (4). This has a channel which forms part of the recycle line and the inlet (1 1 ) and outlet (12) connections for the recycle line are shown. A third channel forms part of the feed line with connection (13). Different connection orientations can be used. The preferred arrangement is as shown with a straight channel for the recycle line and the feed channel intersecting with this at between 45° and 135° but preferably at 90°. An access port (14) is preferred which is used during fabrication and cleaning. The access port is also used for fitting removable feed apertures (15) where used. It is also used for fitting moveable elements which are used for closing or cleaning the feed aperture (15).

The slurry delivery device is preferably mounted so that the recycle channel is horizontal and that the body of the slurry delivery device can be rotated around the long axis of the recycle channel such that the orientation of the feed channel can be varied from bottom dead centre to top dead centre. This angle may be varied to optimise control of the ratio of solids to liquids passing into the feed channel. It is preferred that the angle of feed channel is ±45° from horizontal.

Figure 3 shows a section through the slurry delivery device (4). The feed aperture (15) forms a connection between the recycle line and the feed channel. It is preferred that a transition zone (16) is located between the feed aperture and the feed line. This creates a progressive expansion from the feed aperture with flaring at an angle of 45° or greater.

The slurry delivery device (4) diverts fluid from the recycle line (2) to the feed line (5) with the same ratio of solids to liquid as is in the feed tank (1 ). The key requirements for this are described below.

The feed aperture (15) is circular with a diameter of less than 10mm and preferably less than 5 mm. The length of the feed aperture is equal to or less than the diameter of the aperture and more preferably equal to or less than half the diameter. The length of the feed aperture preferably does not exceed 5 mm. The feed aperture has no pockets. The feed aperture preferably has a horizontal surface of less than 3 mm and more preferably less than 1 mm. The feed aperture is polished with no projections to trap particles. It is preferred that any sharp edges of the aperture are removed. The diameter of the feed aperture is selected to be greater than 4X and more preferably greater than 8X the diameter of the particles in the slurry. It is preferred the cross sectional area of the aperture is less than 25% that of the feed (5) line and more preferably less than 18%. It may be connected above or at the midpoint or below the midpoint of the recycle channel. It is preferred that the diameter of the feed channel (15) may be constant although it is preferred that it is flared with the diameter increasing from the recycle side to the feed side at an angle of 45° or less. The channel may be cut into the body of the slurry delivery device although a separate insertable element is preferred so that the orifice size can be changed within the same device. The insertable element may also incorporate a transition zone. The insertable element is inserted via the access port (14)

The slurry delivery device (4) is a type of valve for controlled transfer of slurry. It is preferred that the aperture and the channel (15) have minimum horizontal surfaces and preferably zero horizontal surfaces in the operating position such that there is a constant fall between the recycle line (2) and the aperture on one side and a constant fall between the aperture and the feed line (5) on the other side. The slurry delivery device (4) requires mechanical strength to operate at elevated pressures. These pressures can be 50 bar and more preferably 100 bar or more. Within the device are intersecting channels with minimal distance between the perimeter of the recycle line and the centre of the feed line. For good mechanical strength it is therefore preferred that the recycle line and the feed channel within the dosing element are formed from two and more preferably a single piece of material.

The slurry delivery device (4) is used where the flow conditions in the unmixed zones is laminar. The slurry delivery device may be used for flow rates of less than 100 l/hr and more preferably less than 50 l/hr and even more preferably less than 25 l/hr.

The slurry delivery device (4) is preferably made of materials that are compatible with the process material and of sufficient mechanical strength. Many different materials and combinations of materials can be used. It is preferred that the recycle line is well mixed and this may be achieved through high axial velocities with or without static mixing elements. It is preferred that the flow conditions in the recycle line are turbulent.

It is preferred that the slurry delivery device (4) has no moving parts, although an additional feature of a moving part can be fitted in the form of a pin which can be pushed forward from the feed line side to close the aperture or clear blockages. This pin can be manually operated or automated and is mounted via the access port (14).

Figure 4 shows a slurry delivery device with a gas bleed connection (17). This prevents gas from accumulating in the delivery device. This gas bleed line (not shown) is connected to the gas bleed connection and this line is provided with a means to prevent fluid flowing up the gas bleed line. This can be done by elevating the gas bleed line so that the static head of liquid is too high to overcome or by a mechanism which only permits the passage of gas. Different methods can be used such valves in combination with level detector or floats that block the gas line when the liquid level is high. In the installed position, the gas bleed connection is typically the highest point on the slurry delivery device. It is preferred that it is within 45° of the vertical.

The slurry delivery device can be used for feeding slurries into continuous reactors and is particularly useful for the provision of solid catalysts for continuous reactors.