METERING DEVICE

Abstract

Metering device for metering a readily combustible substance, in particular acrolein acetal, from a source or a container for the substance into a vacuum line (38) by a pump whose pump power is controllable, characterized in that the pump is driven a compressed air motor (28) operated displacement pump (26), and that between the positive displacement pump (26) and the vacuum line (38) a pressure holding and regulating valve is arranged whose dimensionless delivery height H/Ho[mWS/1 mWS] with the dimensionless delivery rate Q/Qo[m.sup.3/h/1 m.sup.3/h] according to the Formula:

{H/Ho}={C1*(Q/Qo)}.sup.0.333, where.

H=Hydraulic pressure at the inlet of the pressure holding and regulating valve
Ho=1 mWS
C1=Constant for the pressure holding and regulating valve
Q=Hydraulic flow rate
Qo=1 m.sup.3/h.

Claims

1. Metering device for metering a readily combustible substance, in particular acrolein acetal, from a source or a storage container for the substance into a vacuum line (38) by a pump whose pump power is controllable, characterized in that the pump by driven by a compressed air motor (28) operated displacement pump (26), and that between the positive displacement pump (26) and the vacuum line (38) a pressure holding and regulating valve is arranged whose dimensionless delivery height H/Ho [mWS/1 mWS] is related with the dimensionless delivery rate Q/Qo[m.sup.3/h/1 m.sup.3/h] according to the formula:
{H/Ho}={C1*(Q/Qo)}.sup.0.333, where. Hydraulic pressure at the inlet of the pressure holding and regulating valve Ho=1 mWS C1=Constant for the pressure holding and regulating valve Hydraulic flow rate Qo=1 m.sup.3/h.

2. Metering device according to claim 1, characterized in that the pressure holding and regulating valve (35) comprises: a cylindrical valve housing (1) with an upper side (2), in which a central inlet bore (3) is provided with a diameter d1, and with a bottom (4), in which an inner bore (5) is provided, whose diameter d2 is greater than that of the diameter d1 of the inlet bore (3) and which forms an outlet of the pressure holding and regulating valve, a closure piston (8) with an upper part (9), whose diameter d3 is smaller than the diameter d2 of the inner bore (5) and larger than the diameter d1 of the inlet bore (3), a freely movable, circular sealing disc (7) made of an elastomer between the closure piston (8) and an inner sealing surface (6) which is formed between the inner bore (5) and the inlet bore (3) on an inner side of the valve housing (1), and by a compression spring (12), which is supported in the inner bore (5) and presses through the closure piston (8) the sealing disc (7) against the inner sealing surface (6).

3. Metering device according to claim 2, characterized in that the sealing disc (7) has a diameter d3 which is greater than the diameter d1 of the inlet bore (3) plus the radial extent of the inner sealing surface (6), and which is smaller than the diameter d3 of an upper part (9) of the closure piston (8).

4. Metering device according to claim 2, characterized in that a gap (16) formed between the upper part (9) of the closure piston (8) and the inner bore (5) has a cross-sectional area corresponding to the cross-sectional area of the inlet bore (3).

Description

[0015] In the drawings:

[0016] FIG. 1 shows a section through a pressure holding and regulating valve which is used in the metering device according to the invention;

[0017] FIG. 2 shows a section through an installation of the pressure holding and regulating valve of FIG. 1 in a process plant;

[0018] FIG. 3 is a schematic representation of a metering device according to the invention for easily combustible substances, in particular acrolein; and

[0019] FIG. 4 is a graph showing the ratio of the compressed air pressure on a compressed air motor of the metering device to the stroke rate of the positive air motor driven by the displacement pump.

[0020] First of all, a pressure holding and regulating valve will be described with reference to FIGS. 1 and 2, which is used in the inventive metering device for a vacuum distillation plant.

[0021] According to FIG. 1, the pressure holding and regulating valve according to the invention has a cylindrical, metallic valve housing 1 with a top side 2 in which a central inlet bore 3 with a diameter d1 is located. The valve housing 1 comprises an inner bore 5, the diameter d2 of which is greater than the diameter of the inlet bore 3 and which forms an outlet of the pressure holding and regulating valve. The valve housing 1 has an underside 4, which, like the upper side 2, is designed as a flat surface and thus can be used as sealing surfaces against connecting components during installation of the pressure holding and regulating valve.

[0022] In the valve housing 1 there is located between the inner bore 5 and the inlet bore 3, a cylindrical, planar, inner sealing surface 6 as a transition between the inner bore 5 and the inlet bore 3. A freely movable, circular sealing disk 7 made of an elastomer, is arranged between a closure piston 8 and the sealing surface 6. As FIG. 1 shows, the diameter d3 of a cylindrical upper part 9 of the closure piston 8 is smaller than the diameter of the inner bore 5 but larger than the diameter of the inlet bore 3.

[0023] The sealing disk 7 has a diameter d3 which is greater than the diameter of the inlet bore plus the radial extent of the sealing surface 6. In addition, the diameter d3 of the sealing disk 7 is smaller than the diameter d4 of the upper part 9 of the closure piston 8. The sealing disk 7 thus closes the inlet bore 3 independently of the lateral position of the sealing disk 7 when the closure piston 8 presses the sealing disk 7 against the sealing surface 6. The closure piston 8 has rounded edges 10. A cylindrical lower part 11 of the closure piston 8 has a smaller diameter d4 than the inner diameter of a compression spring 12, which presses the closure piston 8 via the sealing disc 7 against the sealing surface 6.

[0024] The compression spring 12 has free passage gaps between the turns. The outer diameter of the compression spring 12 is smaller than the diameter d2 of the inner bore. 5 The compression spring 12 is biased by one or more clamping rings 13. The clamping rings 13 sit with an h6-fit in the inner bore 5, which has a H7-fit. A Seeger-Ring 14, which is clamped in a groove 15, keeps the clamping rings 13 pressed against the compression spring 12 by compression. In the installed state, the compression spring 12 exerts a force on the sealing disk 7 by being pre-stressing by means of the closure piston 8, whereby the inlet bore 3 is closed in a liquid-tight manner.

[0025] The compressive force of the compression spring 12 is calculated to the spring constant times compression in mm according to the following formula I:

[00001]$.Math.\left(\mathrm{Formula}.Math..Math.I\right)$$\mathrm{Spring}.Math..Math.\mathrm{constant}.Math..Math.\left(N.Math.\text{/}.Math.\mathrm{mm}\right)=\frac{\mathrm{material}.Math..Math.\mathrm{constant}.Math..Math.\left(N.Math.\text{/}.Math.{\mathrm{mm}}^2\right)*{\left(\mathrm{diameter}.Math..Math.\mathrm{of}.Math..Math.\mathrm{spring}.Math..Math.\mathrm{in}.Math..Math.\mathrm{mm}\right)}^4}{\mathrm{Number}.Math..Math.\mathrm{of}.Math..Math.\mathrm{turns}*{\left(\mathrm{diameter}.Math..Math.\mathrm{of}.Math..Math.\mathrm{spring}.Math..Math.\mathrm{in}.Math..Math.\mathrm{mm}\right)}^3}$

[0026] As can be seen, there are several free variables to achieve the desired spring tension. The hydraulic pressure of the liquid inflowing at the inlet bore 3, causes the sealing disc 7 to lift off from the plane inner sealing surface 6 against the spring force of the compression spring 12 and that liquid flow entering the inlet bore 3 can flow past the closure piston 8, through a gap 16 between the upper part the closure piston 8 and the inner bore 5 and between the turns of the compression spring 12 into the inner bore 5.

[0027] Preferably, the gap 16 has a cross-sectional area which corresponds to the cross-sectional area of the inlet bore 3. During operation of the pressure holding and regulating valve according to the invention, only the spring 12 and the closure piston 8 are moving. The sealing disc 7 therein remains between the closure piston 8 and the sealing surface 6.

[0028] The compression spring 12, the closure piston 8 and the sealing disc 7 can move radially in the outlet bore 5 and locate themselves in free play centrically in the inner bore 5, as experiments show. Therefore, the pressure holding and regulating valve according to the invention can advantageously be used on seagoing vessels, where the ordinate axis performs a tumbling motion by the swell.

[0029] As shown in FIG. 2, the pressure holding and regulating valve may be installed between two DIN flanges 17, 17 using flat gaskets 18, 18. In case the flanges 17, 17 are parts of two shut-off valves, the pressure-holding and regulating valve according to the invention can be easily removed during operation by locking both valves above and below the pressure holding and regulating valve of FIG. 1 and loosening the bolts 19. The disconnected pressure holding and regulating valve is disassembled by taking off the Seeger-Ring 14, and another compression spring 12 or an additional clamping ring 13 can be replaced in a short time.

[0030] The metering device comprises a storage container 20 for a liquid 21 to be transported, for example acrolein acetal. The level of liquid in the storage container 20 may be low, as shown at 22, or high as shown at 23. At the bottom of the storage container 20, a suction line 24 is attached, which leads to a positive displacement pump 26 as a metering pump. The displacement pump 26 is connected via a mechanical coupling 27 with a compressed air motor 28. The compressed air motor 28 is connected to a compressed air line 29 and has an exhaust air pipe 31.

[0031] A pressure line 33 leads directly via a flange 17 to the inlet bore 2 of the pressure holding and regulating valve 36, the inner bore 5 of which opens at a flange 17 of a metering line 39. Through an open shut-off valve 40 the medium pumped through the displacement pump 26, acrolein acetal for example, arrives at the vacuum pipe line 59.

[0032] The positive displacement pump 26 had a capacity of 27 liters per hour at 128 strokes per minute. In vacuum pipe line 59 there was a vacuum of 9.5 mWS (meters of water). At this flow rate of 27 liters per hour, the pressure gauge in the pressure line 33 indicated a pressure of 25 mWS. The compressed air pressure in the compressed air line 25 was 77 kPa.

[0033] As is known, the torque of compressed air motors is non-linear to the compressed air pressure due to the inevitable slip at low pressures of less than 2 bar. Additional measures are therefore required to establish the desired linearity between the compressed air pressure and the stroke rate of the positive displacement pump.

[0034] Experiments have shown that, in the pressure holding and regulating valve of FIG. 1, the relationship between the hydrostatic pressure at the inlet bore 3 and the flow rate through the pressure holding and regulating valve, is the ratio of two pressures equal to the third root of the ratio of the respective two volume flows.

[0035] If H/Ho [mWS/1 mWS] denotes the hydrostatic pressure in dimensionless form and Q/Qo [m.sup.3/h/1 m.sup.3/h] the hydraulic flow rate in dimensionless form, the following formula applies to the pressure holding and regulating valve of the invention:

{H/Ho}={C1.Math.(Q/Qo)}.sup.0.333FORMULA II

where:
H=Hydraulic pressure

Ho=1 mWS

[0036] C1=Constant pressure holding and regulating valve
Q=Hydraulic flow rate
Qo=1 m.sup.3/h

[0037] Through the use of this pressure holding and regulating valve, the desired linearity between the compressed air pressure on the compressed air motor 28 and the number of strokes of the positive displacement pump 26 is obtained.

[0038] As proof of this, the compressed air motor 28 of the metering device according to FIG. 3 was subjected to different pressures of compressed air and the associated number of strokes of the displacement pump 26 was measured. The results are shown in the graph in FIG. 4. The ordinate denotes the strokes per minute of the positive displacement pump 26, and the abscissa denotes the compressed air pressure on the compressed air motor 28. As can be seen from FIG. 4, the use of the pressure holding and regulating valve 36 of FIG. 1 provides a linear stroke/pressure curve, so that the control of the stroke frequency by means of compressed air control is a fully-fledged, hazard-free replacement for the electric frequency converter.

[0039] The following pressure holding and regulating valve according to FIG. 1 was used in the tests, which was defined by the following parameters:

Valve body 1: Material no. 1.2424, outside diameter 27 mm, height=32 mm,
Inlet bore 3: Diameter=8 mm
Inner bore 5: Diameter=19 mm
Closure piston 8: Material no. 1.2424, Diameter upper part 17.2
Sealing washer 7: Viton; Outer diameter 16 mm; Height of plate 2 mm
Spring 12: Material no. 1.2330 Outside diameter 17.25 mm, wire thickness 1.25 mm
Clamping rings 13: Material no. 1.2424, 3 pieces, height 2 mm
Flanges 17: Material no. 1.2771, both sides DN 15

LIST OF REFERENCE SIGNS

[0040] 1 Valve Housing [0041] 2 Upper Side [0042] 3 Inlet Bore [0043] 4 Lower Side [0044] 5 Inner Bore [0045] 6 Inner Sealing Surface [0046] 7 Sealing Disc [0047] 8 Closure Piston [0048] 9 Upper Part Closure Piston [0049] 10 Peripheral Edges [0050] 11 Lower Part Closure Piston [0051] 12 Compression Spring [0052] 13 Clamping Ring [0053] 14 Seeger Ring [0054] 15 Groove for Seeger Ring [0055] 16 Annular Gap [0056] 17 Flange [0057] 17 Flange [0058] 18 Flat Gasket [0059] 18 Flat Gasket [0060] 19 Screw Bolt [0061] 19 Screw Bolt [0062] 20 Reservoir [0063] 21 Delivery Liquid [0064] 22 Liquid Level Flow [0065] 23 Liquid Level High [0066] 24 Suction Line [0067] 25 Flow Direction Suction Line [0068] 26 Displacement Pump [0069] 27 Mechanical Coupling [0070] 28 Compressed Air Motor [0071] 29 Compressed Air Line [0072] 30 Flow Direction Compressed Air Inlet [0073] 31 Exhaust Port [0074] 32 Flow Direction Exhaust Air [0075] 33 Pressure Line [0076] 34 Flow Direction Pressure Line [0077] 35 Pressure Holding and Regulating Valve [0078] 36 Metering Line [0079] 37 Shut-off Valve [0080] 38 Vacuum Pipe