Device For Controlling Thermal Hydrolysis Decompression and Process Plant Comprising Such Device

Abstract

The present invention provides a device for controlling steam explosion of biomass having a dry solids content above 1%, a VS content of above 20%, and including abrasive material, in a pressure relief vessel, which includes one or more blowdown conduits having at their outlets an adjustable open area for regulating the blowdown discharge rate. The adjustable open area of each of the one or more blowdown conduits are constructed in such a way that expansion/spray due to flashing takes place either inside the pressure relief vessel itself or in an additional inlet device through which the discharged biomass is directed from the adjustable open area and into the pressure relief vessel and which either have a large enough dimension to avoid the discharged biomass hitting essential parts of the construction or is made from a highly resistant/durable material.

Claims

1.-24. (canceled)

25. A device for relieving the pressure of biomass upon entering a pressure relief vessel, the biomass being in the form of moist material including abrasive material having a particle size >150 micron and rated at 7 or above on Mohs scale of hardness, and having a dry solid content above 5% whereof above 20% is volatile solids (VS), the device comprising one or more blowdown conduits for transporting said biomass in the form of moist material from said reactor to said pressure relief vessel and discharging said biomass in the form of moist material into said pressure relief vessel, wherein: said blowdown conduits are either oriented towards a sacrificial material or already discharged biomass collected inside said pressure relief vessel, or arranged in one or more vessel-inlet-nozzle/devices to said pressure relief vessel either made from a highly durable material or having a dimension large enough to avoid discharged biomass hitting any parts of said one or more vessel-inlet-nozzle/device, and said one or more blowdown conduits are provided at the outlet thereof with valves having a variable cross-sectional area providing an adjustable open area for: a) regulating the blowdown discharge rate of said biomass in the form of moist material into said pressure relief vessel, and b) providing the smallest cross sectional/opening area of said one or more blowdown conduits at the outlet of said one or more blowdown conduits.

26. The device according to claim 25, wherein said valves being adapted at said outlet of said one or more blowdown conduits are an integral part of said one or more blowdown conduits.

27. The device according to claim 25, comprising a plurality of blowdown conduits each being adapted with valves at said outlet of said blowdown conduits.

28. The device according to claim 25, wherein said valves are in the form of a valve arrangement comprising: a supporting element affixed to a wall of said blowdown conduit; a displaceable rod adapted to cooperate with said supporting element; a movable part mounted on said adjustable rod; and a static part having a shape corresponding to that of the movable part for blocking the flow of said biomass in the form of moist material upon contact with said movable part.

29. The device according to claim 28, wherein said movable part is a cone which defines a cone slope, and said shape of the static part corresponding to that of the movable part defines a slope which is equal to, or higher than said cone slope.

30. The device according to claim 28, wherein said movable part is made of material with high erosion resistance, such as silicon carbide (SiC).

31. The device according to claim 25, wherein one or more of said one or more blowdown conduits comprise a first pipe and a second pipe which are mutually rotatable, said first pipe being provided with a close sliding fit inside said second pipe, said first and second pipe defining holes/apertures that overlap depending on the pipe being rotated for varying said adjustable open area.

32. The device according to claim 25 further comprising a mesh with smaller openings than the smallest cross sectional/opening area of said one or more adjustable open areas at the outlet of said one or more blowdown conduits, said mesh being placed upstream of the outlet of said one or more blowdown conduits.

33. A plant for producing a pretreated biomass by subjecting raw biomass to thermal hydrolysis, said plant comprising a thermal hydrolysis reactor for producing biomass under pressure in the form of a moist material including abrasive material having a particle size >150 micron and rated at 7 or above on Mohs scale of hardness, and having a dry solid content above 5% whereof above 20% is volatile solids (VS), a pressure relief vessel in fluid communication with said reactor for relief of pressure of said moist material, and one or more devices according to claim 25.

34. A method for thermal hydrolysis of raw biomass comprising: subjecting said raw biomass to thermal hydrolysis thereby producing biomass in the form of a moist material under pressure; and transferring said biomass to a pressure relief vessel for relief of pressure of said moist material; characterized in that: said moist material has a dry solid content above 5% whereof above 20% is volatile solids (VS) and that it includes abrasive material having a particle size >150 micron and rated at 7 or above on Mohs scale of hardness, and said transfer of said biomass to said pressure relief vessel is achieved by use of a device comprising one or more blowdown conduits for transporting said biomass in the form of moist material from said reactor to said pressure relief vessel and discharging said biomass in the form of moist material into said pressure relief vessel, wherein said one or more blowdown conduits either oriented towards a sacrificial material or already discharged biomass collected inside said pressure relief vessel, or arranged in one or more vessel-inlet-nozzle/devices to said pressure relief vessel either made from a highly durable material or having a dimension large enough to avoid discharged biomass hitting any parts of said one or more vessel-inlet-nozzle/device, and wherein said one or more blowdown conduits are provided at the outlet thereof with valves having a variable cross-sectional area providing an adjustable open area for: a) regulating the blowdown discharge rate of said biomass in the form of moist material into said pressure relief vessel; and b) providing the smallest cross sectional/opening area of said one or more blowdown conduits at the outlet of said one or more blowdown conduits.

35. The method according to claim 34, wherein said valves are oriented towards one or more wear plates, wear devices, deflection plates or similar pieces of equipment.

36. The method according to claim 34, wherein said one or more valves are in the form of a valve arrangement comprising: a supporting element affixed to a wall of said blowdown conduit; a displaceable rod adapted to cooperate with said supporting element; a movable part mounted on said adjustable rod; and a static part having a shape corresponding to that of the movable part for blocking the flow of said biomass in the form of moist material upon contact with said movable part.

37. The method according to claim 36, wherein said movable part is a cone which defines a cone slope, and said shape of the static part corresponding to that of the movable part defines a slope which is equal to, or higher than said cone slope.

38. The method according to claim 36, wherein said movable part is made of material with high erosion resistance, such as silicon carbide (SiC).

39. The method according to claim 34, wherein one or more of said one or more blowdown conduits comprise a first pipe and a second pipe which are mutually rotatable, said first pipe being provided with a close sliding fit inside said second pipe, said first and second pipe defining holes/apertures that overlap depending on the pipe being rotated for varying said adjustable open area.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] FIG. 1A shows a schematic layout of a pressure relief vessel i.e. flash tank according to the prior art.

[0061] FIG. 1B shows a schematic layout of a pressure relief vessel i.e. flash tank according to the present invention.

[0062] FIG. 2 shows the flow rate, i.e. the discharge rate of moist material (mixture of steam an organic material) through a nozzle versus nozzle diameter according to the prior art.

[0063] FIG. 3A shows erosion of a pipe on the discharge side of a blowdown nozzle according to the prior art.

[0064] FIG. 3B shows the discharge side (FIG. 3Ba) and entry side (FIG. 3Bb) of a blowdown nozzle according to the prior art, thus having a piping upstream and downstream the nozzle.

[0065] FIG. 4 shows scaling caused by the drying effect of superheated steam in the piping downstream a control valve, in accordance with the prior art.

[0066] FIGS. 5A, 5B and 5C show a particular embodiment according to the first aspect of the present invention, where the valve is located at the end of the blowdown conduit, i.e. at the outlet or tip thereof.

[0067] FIG. 6 shows another particular embodiment according to the first aspect of the present invention, where the blow conduit comprises two rotating pipes (side view). Maximum opening corresponds to coincidence of the holes of the pipes.

DETAILED DESCRIPTION

[0068] FIG. 1A shows a typical pressure relief vessel, i.e. flash tank 10. High-pressure steam explosion is a process of rapid release of pressurized water or water-rich material 12 as shown by the arrow, normally conducted through a nozzle or an orifice. This process is known also as blowdown, explosive decompression, rapid depressurization, etc. and results in a rupture of the moist material and make it more accessible for subsequent processes, e.g. digestion or dewatering. For this purpose, a raw substrate is first compressed in a reactor, passes through the blowdown conduit 14 and then discharges from a nozzle 16 of the blowdown conduit 14 into the pressure relief vessel 10. The flow rate through the nozzle, i.e. the blowdown discharge rate of the moist material, depends on many parameters such as inlet and outlet pressures, critical pressure and molar volume of the substrate, orientation of the vessels, location of the nozzle, discharge coefficient, etc. The blowdown conduit includes also a valve 18, which according to the prior art would normally be located between the reactor (not shown) and the pressure relief vessel 10 (FIG. 1A), whereas in a device according to the present invention this would be in a position where the valve gate coincides with the tip or the end, of the blowdown conduit (FIG. 1B). Hence in a device according to the present invention there should either be no piping downstream of the valve 28 (FIG. 1B) or the valve should be fitted with a vessel-inlet-nozzle/device (i.e. an additional inlet device through which the discharged biomass is directed from the adjustable open area into the pressure relief vessel) having either a large enough dimension to avoid expansion/spray hitting essential parts of the construction and thereby causing erosion, or made from a highly resistant/durable material, such as e.g. silicon carbide. After steam explosion, substrate being discharged is collected as a liquid 20 in the flash tank and defines a liquid level 22. The flash tank 10 comprises also a conduit for allowing a flash stream 24 to exit with the aid of valve 26 and a conduit 27 allowing for the exit of the liquid 20 from the vessel.

[0069] A series of large-scale measurements of the blowdown rate as a function of the cross-sectional area of the nozzle 16 and inlet pressure for a chosen design has been performed. In all experiments, substrate 12 containing 13% dry solids originating from municipal sludge or food waste was transferred from the reactor to a blowdown nozzle 16 with minimal pressure losses. The blowdown nozzle 16 of different diameters was placed in a vertical position in the upper area as shown in the figure and inside the flash tank 10 and oriented towards already treated liquid material 20. The line prior to the blowdown nozzle 16 was relatively large (110 mm Ø) and the minimum open area of the nozzle was located at the very tip of the blowdown nozzle 16. The diameter of the flash tank 10 was larger than 1400 mm Ø. The flow rate through the blowdown nozzle 16 was calculated as the ratio of the volume of the liquid in the reactor to the blowdown time, which were estimated based on the pressure sensor readings and level measurement in the pressure relief vessel.

[0070] FIG. 2 shows the results for different diameters of the nozzle. The circle and square symbols correspond to the inlet pressure of 7 and 6 bar, respectively. The X-axis shows the nozzle diameter in mm and the Y-axis shows the average flow rate in kg/m2/s. The outlet pressure was fixed at 2 bar. As can be seen the experiments confirmed that the discharge rate is directly proportional to the cross-sectional area of the nozzle and decreases with the inlet pressure. However, the determination of the actual flow rate as e.g. ˜140 kg/m2/s at an inlet pressure of 7 bar and an outlet pressure of 2 bar allows for the determination of the flow coefficient (C.sub.V), as a function of the cross-sectional area.

[0071] C.sub.V can be computed as follows:

[00001]$C_V=0.366.Math.Q\sqrt{\frac{G_L}{P_1-P_2}}$

where Q is the volumic flow rate (m3/h); G.sub.L is the liquid relative density (taken as 1); P.sub.1 and P.sub.2 are the inlet and outlet pressure, respectively.

[0072] Knowledge of the relationship between flow coefficient (C.sub.r) and cross-sectional area makes it possible to control the discharge rate at different valve openings for a given moist material, in this case municipal sludge or food waste containing 13% dry solids

[0073] The average velocity through the choke point in the nozzle for liquid and the two-phase gas and liquid flow prior to and after steam explosion is calculated as 7 m/s and 500 m/s, respectively.

[0074] It should be noted, that harsh operation conditions cause undesirable changes in the equipment and thus affect the performance, durability and reliability of the plant. Among them, we identify those caused by erosion, scaling and blockage.

[0075] Re. Erosion:

[0076] To prevent erosion the fluid velocity in pipework or a vessel should not exceed a certain value depending on the material. Our observations show that the erosion rate in 316 stainless steel is negligible for the average steam velocities below 20 m/s. However, under the conditions of the experiment described above, the average velocity after steam explosion is about 500 m/s, i.e. more than one order of magnitude higher.

[0077] Mandipoor et al. (Scientific Reports 5: 14182 (2015) www.doi.org/10.1038/srep14182) have investigated the impact of high-speed water droplet of different sizes on the erosion of titanium alloys. Their experiments revealed a power law dependence (ER˜V.sup.n) between the erosion rate and droplet speed. Here n is between 7-13 depending on the alloy composition. Particularly, the results indicate that 1 mm.sup.3 of water droplets at V=275-350 m/s causes 10.sup.−6-2×10.sup.−4 mm.sup.3 of the material loss. Here the material loss is defined as the difference in volume between the as-received specimen and the eroded specimen. In the context of the present invention, even a greater erosion rate may occur, since the discharge stream contains inorganic abrasive particles such as sand and its velocity is higher.

[0078] To quantify the erosion rate under our conditions the following experiment was conducted. A pipe made of 316 stainless steel with an outer diameter of 88 mm and wall thickness of 15 mm was installed directly after a blowdown nozzle made of hardened carbon steel. The inner diameter of the pipe downstream the nozzle was 58 mm while the blowdown nozzle had an inner diameter of 36 mm. This results in a distance of 11 mm from the opening of the blowdown nozzle to the pipe wall. The pressure and temperature on the entry side and discharge side of the blowdown nozzle was 7 bar and 165° C. and 2 bar and 120° C., respectively. There were no visible or measurable signs of erosion in the blowdown nozzle or on the entry side of the nozzle after a total blowdown time of about 1000 hours. In the same plane as the end of the blowdown nozzle, the downstream pipe appeared to be polished, but there was no measurable loss of material. However, at 23 mm distance from the blowdown nozzle, the originally 15 mm thick steel pipe was completely eroded, and a sharp edge was formed. This erosion pattern is illustrated in FIG. 3A.

[0079] FIG. 3Ba shows the discharge side and FIG. 3Bb shows the entry side of the blowdown nozzle made of hardened carbon steel and having piping upstream and downstream the nozzle. Similar erosion might take place downstream control valves if there is insufficient distance to any solid surfaces downstream the plane where development of flash steam takes place. Furthermore, this illustrates the difficulties with using a control valve with piping upstream and downstream the valve to regulate the discharge rate from a reactor in a THP plant.

[0080] To avoid destructive contact between the fluid stream and walls of the flash tank, the blowdown nozzle is oriented towards already treated liquid material. For the same reason the distance between the blowdown nozzle and the liquid level (see FIG. 1) should be large enough due to possible splashing inside the flash tank.

[0081] Re. Scaling:

[0082] In a different test a pipe with an inner diameter of 57 mm was placed after a control valve used to control the discharge rate for a THP reactor. Municipal sludge at about 8% DS was discharged at an average rate of about 0.05 m.sup.3/min through the control valve. This results in superheating of the flash steam which facilitates drying of solid material attached to pipe walls. This causes scaling and eventually blockages in piping downstream the control valve as shown in FIG. 4.

[0083] The effects of scaling can be mitigated by placing the blowdown nozzle or the part of a control valve used to regulate the discharge rate at the very end of pipework located inside a significantly larger pipe or inside a pressure vessel. Scaling will also occur in such a scenario, but formation of scaling is a relatively slow process. If the pressure relief vessel or piping downstream the control valve or restriction has a sufficiently large diameter, then scaling needs to be removed at reasonable time intervals such as during planned and scheduled annual maintenance stops.

[0084] Re. Blockages

[0085] To prevent blockages, a mesh with smaller openings than the open area of a static nozzle or the smallest opening in an adjustable nozzle must be in place upstream of the the open area of a static nozzle or the smallest opening in an adjustable nozzle. Alternatively, the inlet pipe can face a surface at a distance smaller than the smallest opening size in a static or adjustable blowdown nozzle. When the discharge device shown in FIG. 1B is only partially open, the distance from the static part to the movable part can be as small as a few millimeters. If particles become stuck in the device, the movable part can be lifted to a position where the opening of the static part will have the smallest diameter of any section where substrate is present prior to the outlet. This will make it possible to dislodge stuck particles to reestablish flow through the nozzle by retracting the movable part. With this configuration, particles larger than those that can be passed through the blowdown nozzle remain in the reactor and are removed during scheduled maintenance stops.

[0086] Now, with reference to FIG. 5, a device for adjusting the blowdown rate according to the present invention is shown. In FIG. 5A, the adjustable valve 28 at the outlet of the blowdown conduit 14 as shown in the figure, includes of a movable part 30 mounted on an adjustable rod 32 and a static part 34 which repeats the shape of the movable part 30 to block the fluid flow upon contact with the movable part 30. The static part 34 as shown by the hatched area is permanently fixed to wall of the blowdown conduit 14, this preferably being in form of a thick-walled pipe 36, while the movable part 30 can travel, preferably only vertically, by displacing the rod as shown by the arrows. A supporting element 38 affixed to the wall of the blowdown conduit 16, preferably as rod support rings prevent any movements except the vertically applied displacements. In this example, the tip of the movable part 30 is a right circular cone with radius R and height H. The distance 2R corresponds to the opening at the outlet as also shown in the figure. The fluid passes through a cross-sectional area (S) formed between the cone and the static part. This can either be a circular ring created by rotating the segment AC (see FIG. 5B) around the vertical axis or a lateral surface of a newly formed cut cone with a slant height of AB (see FIG. 5C). Mathematically, this can be expressed as:

[00002]$S=\min \left(S_{\mathrm{AB}},S_{\mathrm{AC}}\right)=\min \left(\frac{\pi R\left(H-h\right)\left(H\left(h+H\right)+2R^2\right)}{\sqrt{1+H^2/R^2}\left(H^2+R^2\right)},\pi R^2-\frac{\pi h^2{R}^2}{H^2}\right),\mathrm{for}h=0..H.$

[0087] Here h describes the vertical position of the movable part 30 with respect to the static part 34 and is chosen such that h=H when the cone is completely pressed to the static part.

[0088] Such arrangement helps to prevent development of flash steam prior to the outlet of the device. In this context, it is advantageous to make the cone in a hard material such as silicon carbide to minimize erosion rates as this part will be subject to the most violent operation conditions.

[0089] It is preferred, that the slope of the movable part (cone) 30 (tan.sup.−1R/H) is steeper compared to the static part 34. This ensures that the minimum open cross-sectional area always coincides with the circular ring (S.sub.AC) of the blowdown nozzle. As a result, the wear and tear on the static part is reduced with increasing of protrusion of the movable part 30 into the steam explosion zone, as also shown in FIG. 5A, and thereby imposing an extra load on the movable part 30.

[0090] With reference to FIG. 6, another embodiment according to the invention is shown by fitting a pipe with a close sliding fit inside a somewhat larger pipe where both pipes have holes that will overlap depending on the position of the pipe that can be rotated as also shown in in the figure. By rotating one pipe, the effective open area can be adjusted.

[0091] The present invention thus encompasses a detailed arrangement of a valve to regulate the flow rate under the decompression. This is most relevant for a continuous THP plant but can also be used for batch process plants. A key feature of the device according to the present invention compared to the prior art is the improved resistivity to erosion and blockage, by the adjustable valve controlling the discharge rate being placed at the outlet end of the blowdown conduit (blowdown line).

LIST OF PARTS

[0092] 10 Pressure relief vessel (flash tank) [0093] 12 Moist material (biomass, substrate) [0094] 14 Blowdown conduit [0095] 16 Blowdown nozzle [0096] 18 Valve [0097] 20 Liquid collected in flash tank 10 [0098] 22 Liquid level [0099] 24 Flash stream [0100] 26 Valve [0101] 27 Sludge outlet conduit [0102] 28 Valve arrangement at outlet of blowdown conduit 14 [0103] 30 Movable part [0104] 32 Adjustable rod [0105] 34 Static part [0106] 36 Thick-walled pipe [0107] 38 Supporting element