ENHANCED PRESSURISING OF BULK MATERIAL IN LOCK HOPPERS

Abstract

A process for pressurizing bulk material in an apparatus for pressurizing bulk material in a hopper; wherein the hopper is configured as a lock hopper containing a bulk material, wherein the apparatus comprises a source of pressurized gas, lines to convey the pressurized gas from the source of pressurized gas to one or more inlets of the lock hopper, a valve arrangement arranged in the lines, wherein the process is characterized in that said valve arrangement comprises at least two valves arranged in parallel, each valve being connected to a downstream Laval tuyere, and in that said valves are controlled to open in an operating sequence to provide pressurizing gas with an adjusted gas flow rate to the lock hopper.

Claims

1. A process for pressurizing bulk material in an apparatus for pressurizing bulk material in a hopper; wherein the hopper is configured as a lock hopper containing a bulk material, wherein the apparatus comprises a source of pressurized gas, lines to convey the pressurized gas from the source of pressurized gas to one or more inlets of the lock hopper, a valve arrangement arranged in the lines, wherein said valve arrangement comprises at least two valves arranged in parallel, each valve being connected to a downstream Laval tuyere, said method comprising: controlling said valves to open in an operating sequence to provide pressurizing gas with an adjusted gas flow rate to the lock hopper.

2. The process as claimed in claim 1, wherein the opening of the at least two valves in the operating sequence is controlled based on an actual gas flow rate of the pressurizing gas measured downstream the valve arrangement using a volume flow rate or velocity measurement device and/or on a gas flow rate of the pressurizing gas calculated based on actual upstream and downstream pressures measured using a pressure sensing device during the pressurizing.

3. The process as claimed in claim 1, wherein the source of pressurized gas is a gas supply main and/or an intermediate buffer vessel arranged between the gas supply main and said valve arrangement.

4. The process as claimed in claim 2, wherein the Laval tuyeres in the valve arrangement have different inner cross-sections and wherein the operating sequence comprises opening and closing the valves of the valve arrangement allowing for further adjusting the actual gas flow rate of the pressurizing gas.

5. The process as claimed in claim 3, wherein a further line from the gas supply main to the one or more inlets of the lock hopper comprises a valve connected to a downstream Laval tuyere, which valve is controlled to open within the operating sequence by an end of the pressurizing.

6. A valve arrangement comprising: at least two valves arranged in parallel, each valve being connected to a downstream Laval tuyere, and a control unit configured to control an opening of said valves in an operating sequence to provide pressurizing gas with an adjusted gas flow rate to a lock hopper in an apparatus for pressurizing bulk material in a hopper.

7. The valve arrangement as claimed in claim 6 configured for accelerated pressurizing bulk material in a hopper.

8. The valve arrangement as claimed in claim 6 configured for reducing noise nuisances and/or wear in pressurizing bulk material in a hopper.

9. The valve arrangement as claimed in claim 6 configured for reducing bulk material compacting during pressurizing bulk material in a hopper.

10. The valve arrangement as claimed in claim 6 configured for operating an existing apparatus for pressurizing bulk material in a hopper at higher pressure differential between pressurized gas source and unpressurized hopper.

11. The valve arrangement as claimed in claim 6 disposed in an existing conventional apparatus for pressurizing bulk material in a hopper for operating said existing conventional apparatus for pressurizing bulk material in a hopper at lower pressure differential between pressurized gas source and pressurized lock hopper.

12. An apparatus for pressurizing bulk material in a hopper, comprising: a hopper configured as a lock hopper for containing a bulk material, a source of pressurized gas, lines configured to convey the pressurized gas from a source of pressurized gas to one or more inlets of the lock hopper, a valve arrangement arranged in the lines, wherein the valve arrangement comprises at least two valves arranged in parallel, each valve being connected to a downstream Laval tuyere, wherein the opening of each of said valves is controllable by a control unit, wherein the control unit is configured to control the opening of the valves in an operating sequence in order to provide pressurizing gas with an adjusted gas flow rate to the lock hopper.

13. The apparatus as claimed in claim 12, wherein the opening of the at least two valves of the valve arrangement in the operating sequence is controllable by said control unit based on an actual flow rate of the pressurizing gas measured downstream the valve arrangement using a volume flow rate or velocity measurement device and/or on a volume flow rate of the pressurizing gas calculated based on actual upstream and downstream pressures measured using a pressure sensing device during the pressurizing.

14. The apparatus as claimed in claim 12, wherein the source of pressurized gas is a gas supply main and/or an intermediate buffer vessel arranged between the gas supply main and said valve arrangement.

15. The apparatus as claimed in claim 12, wherein the Laval tuyeres in the valve arrangement have different inner cross-sections and wherein the operating sequence is controllable to allow for independently opening and closing the valves of the valve arrangement to adjust the actual gas flow rate of the pressurizing gas.

16. The apparatus as claimed in claim 12, wherein a line from the gas supply main to the one or more inlets of the lock hopper comprises a valve connected to a downstream Laval tuyere, which valve is controllable by the control unit to be opened within the operating sequence by the end of the pressurizing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Preferred embodiments of the disclosure will now be described, by way of example, with reference to the accompanying drawing in which:

[0036] FIG. 1 is a schematic diagram of an embodiment of a preferred apparatus of the present disclosure or useable in a process of the present disclosure and

[0037] FIG. 2 is a graph showing lock hopper pressure and gas volume flow rate as a function of time during lock hopper pressurizing.

[0038] Further details and advantages of the present disclosure will be apparent from the following detailed description of several not limiting embodiments with reference to the attached drawing.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0039] With reference to FIG. 1, an apparatus for pressurizing bulk material in a hopper configured as a lock hopper 29 is provided for containing a bulk material, such as coal powder. A number of lines 22, 26, 28 are provided to convey the pressurized gas from the source (directly or via a buffer vessel) to one or more inlets 30 of the lock hopper 29. A valve arrangement 34 with valves 34A, 34B, 34C, as well as a valve 35 are arranged in the lines and their opening and closing may be controlled by a control unit (not represented separately). This control unit is programmed to control the opening and closing of the valves in an operating sequence in order to provide pressurizing gas to the lock hopper at an adjusted flow rate to the sintered metal discs 30 and the bulk material inside the lock hopper 29. It is important to note that in FIG. 1, additionally or alternatively, valve 35 could also be a valve arrangement in the sense of the present disclosure, such as that shown for valve 34.

[0040] The valves (preferably simple open/closed valves) may be operated in an operating sequence which is preset based on the dimensions of the apparatus and the known pressures of the main supply/buffer vessel and of the lock hopper. Preferably however, the gas volume flow rate is controlled by an operating sequence which takes into account actual parameters during the pressurizing cycle. This may be done by different means or ways.

[0041] A volume flow rate (or velocity) measurement 31 is installed in the pressurizing gas pipeline connecting the buffer vessel 27 to the lock hopper 29. The control unit acts on the valves 34A, 34B, 34C to open a (further or a different) valve if the actual volume flow rate value measured in the measurement 31 drops too far below a preset value.

[0042] Alternatively or additionally, the characteristics of the valves 34A, 34B, 34C, with their associated Laval tuyere, e.g. the mass flow rate produced by the valve depending on the pressure level measured upstream 32, the pressure level measured downstream 33 and the open or closed position of the at least two valves, are included into the controller. The actual mass flow rate value, conditioned by the pressure level measured in 32 and/or 33, is continuously computed. The controller actuates the valves accordingly (by opening further valve or by opening valve with larger associated Laval tuyere and optionally closing the previously open smaller sized line), in such a way as to produce a sequentially increasing mass flow rate, the set point value for the valve position resulting from the pressure levels upstream 32 and downstream 33 and the mass flow rate value.

[0043] The pressurizing gas volume flow rate directly supplied from the process gas supply main 21 may be controlled using valve 35, the pressure upstream now being the pressure level in that process gas supply main.

[0044] As an illustration of the achievements of the present disclosure, the following calculation can be made: pi being the initial (absolute) pressure level in the lock hopper, p.sub.2 the final (absolute) pressure level in the lock hopper, and pressurizing being performed either with constant mass flow rate (by means of a Laval tuyere with constant upstream pressure level), with a volume flow rate adjusted by means of a valve arrangement controlled as described herein or with constant volume flow rate. A corresponding illustrative example is also depicted in the graph of FIG. 2 (see below).

[0045] The maximum actual gas velocity in case of constant mass flow rate pressurizing equaling the actual constant gas velocity in case of constant volume flow rate pressurizing, the ratio of pressurizing time durations of constant volume flow rate pressurizing versus constant mass flow rate pressurizing equals In(p.sub.2/p.sub.1)/[(p.sub.2p.sub.1)/p.sub.a], p.sub.a being the (absolute) atmospheric pressure, In being the natural logarithm. Example: p.sub.1=0 bar g=1 bar a, p.sub.2=9 bar g=10 bar a, p.sub.a=0 bar g=1 bar a. The ratio of pressurizing time durations becomes In(p.sub.2/p.sub.1)/[(p.sub.2p.sub.1)/p.sub.a]=0.256, i.e. the pressurizing time duration would be reduced by up to about 74%.

[0046] FIG. 2 graphically shows the results in terms of hopper pressure and gas volume flow rate as a function of time for a valve arrangement with two valves (2YD), curves (3) and (7) and for a valve arrangement with three valves (3YD), curves (4) and (8), compared to a conventional one valve+Laval tuyere configuration (1YD), curves (1) and (5). All shown variants are based on the following assumptions: pressurizing gas vessel of 65 m.sup.3 useful volume and an initial pressure of 17 bar a; lock hopper to be pressurized having an available gas volume of 22 m.sup.3 and a final pressure of 12 bar a, maximum gas volume flow rate of 3.54 m.sup.3/s to be respected. As can be seen in FIG. 2, even when using two or three Laval tuyeres instead of one, the pressurizing time can already be significantly reduced (from 76 s to only 28.7 s or even only 20.5 s) while respecting the same maximum gas flow rate (i.e. gas velocity).

[0047] Although the pressurizing duration may be reduced to a lesser extent using a valve arrangement as described herein compared to a constant volume flow rate assumption (indicated VAC in FIG. 2, curves (2) and (6)), the reduction is nevertheless hugely significant and surprising, all the more so because these reductions are achieved using technically simple, robust and known components (on/off valves and Laval tuyeres) with a relatively simple control unit.

[0048] The present disclosure is not restricted to embodiments and to specific applications relating to injecting coal into a blast furnace. It may also be applied to other installations comprising pressurized hoppers containing powder materials and requiring periodic pressurization of said hoppers.