WO2017221005A1

WO2017221005A1 - Flare with spuds

Info

Publication number: WO2017221005A1
Application number: PCT/GB2017/051812
Authority: WO
Inventors: Mark HARRADINE
Original assignee: Syngas Products Limited
Priority date: 2016-06-21
Filing date: 2017-06-20
Publication date: 2017-12-28
Also published as: EP3472516A1; GB201709872D0; GB2553412A; GB2553412B; GB201610845D0

Abstract

A flare stack for use in burning off the gas products produced by a pyrolysis system comprises ariser pipe having an inlet for the entry of gas and an outlet from the exit of gas that is located at an upper end of the pipe, and a plurality of flare tips, each comprising a hollow body in fluid communication with the upper end of the riser pipe. The flare tips are each provided with a mechanical non-return valve that is normally closed and which opens when the pressure of the gas flowing along the pipe exceeds a defined level. The invention provides a stack with a high turn down ratio.

Description

FLARE WITH SPUDS

The present invention relates to flare stacks especially, but not exclusively, for use in burning off synthetic gas produced in a pyrolysis process.

Flare stacks are used in a wide range of systems where it is desired to safely dispose of excess gas. Gas enters the flare stack and is burnt in a flame as it exits. A pilot light located at the flare tip ensures it does not blow out, and an air inlet at the base of the stack ensures a good mix of syngas and air to give a safe flame temperature.

One application of flare stacks is in the disposal of hydrocarbon gas produced when waste material, such as municipal derived waste (MDW) and refuse derived fuel (RDF) including wood and pellets, crops and other agricultural waste are used to generate synthetic gas in a pyrolysis system.

In a known pyrolysis process, a feedstock of combustible organic material is fed into a heated pyrolysis kiln. Suitable feedstocks include municipal sourced waste (MSW) and refuse derived fuel (RDF) and also include wood and pellets, crops and other agricultural waste . Heat from a furnace that surrounds the kiln heats the feedstock material to a temperature at which pyrolysis of the material occurs. During this heating it is important that the flow of air into the kiln is prevented, as otherwise the heated pyrolysis gases and char would combust and prevent the production of syngas, and in extreme circumstances may cause an explosion.. The pyrolysis process converts the organic material into char by releasing volatile pyrolysis gases and tars and an amount of fine carbon particulates.

The pyrolyser may be a rotary kiln type pyrolyser as described in GB2441721 B which is incorporated herein by reference . This document describes a rotary kiln having an inlet stage and outlet stage, and a rotary kiln. The inlet stage is upstream of the kiln which is in turn upstream of the outlet stage. A rotary seal on the inlet and a rotary seal on the outlet stage prevents air entering the kiln. The kiln typically slopes down from the inlet to the outlet to encourage the feedstock that enters through the inlet to move out of the outlet. The dust laden pyrolysis gases, which may also contain evaporated oils and water vapour, is removed from an outlet stage of the kiln and passed through one or more filters. The filter must be able to cope with high temperatures and may be a ceramic filter of the kind described in GB2409655B which is also incorporated herein by reference . The ceramic filter is located within a vessel and is scrubbed by a set of rings that can be moved up and down the outer wall of the cylindrical filter element. This removes the solids such as char and entrained dust from the gas.

The filtered gas is then passed through a quencher which cools the gas in a controlled manner causing any entrained tars, oils and water to condense and drop out of the gas to leave a relatively pure synthesized gas known as syngas. This gas can then be burnt to drive a heat engine, such as a gas turbine, in order to generate electricity, or may be partially used as fuel for the furnace, or simply stored for later use or sale .

The solids that are separated from the gas by the filter, in the form of char, may also be used to extract further energy. They may typically be fed to a gasifier which again heats the solids but in this team in the presence of both oxygen (as pure oxygen or in air) and steam, and this gasification extracts any remaining gases and turns the char into ash. These extracted gases, also a form of syngas, may be used as fuel to heat the pyrolyser kiln.

A range of different gasifiers may be used. In the example taught in GB2409655B the gasification takes place towards the top end of the gasifier, and the ash that is left over from the process falls down to the bottom where it can be removed, cooled and bagged.

The use of the pyrolysis process enables the energy contained in the feedstock to be extracted and put to use rather than the traditional process of sending the waste to a landfill site . Because the gases and other waste products can be carefully contained and not emitted into the atmosphere, the process is far cleaner than other combustion processes such as an incineration of organic feedstocks.

The flare stack is an essential part of a typical pyrolysis system. There may be times when the engine is not working, or when the gas is being produced at a rate that is too high for the engine to consume. In each case, if the gas cannot be stored it must be disposed of safely without entering the atmosphere. This can be achieved by diverting the gas to a flare stack, where it is mixed with air and burnt to break down the complex hydrocarbons.

To ensure the flame is not extinguished, it is commonplace to vary the amount of air fed into the flare stack to control the temperature. An air inlet at the base of the stack which can be manually or automatically controlled may be provided. Flare stacks in which the amount of air can be varied are said to have a high turn down ratio as they can cope with a range of different gas flow rates without the flame blowing itself out of burning back down the stack.

The present invention aims to ameliorate at least one limitation on prior art flare stacks where they are to be used to safely burn off waste gas produced in a pyrolysis system. According to a first aspect the invention provides a flare stack for use in burning off the gas products produced by a pyrolysis system, the flare assembly comprising:

A riser pipe having an inlet for the entry of gas and an outlet from the exit of gas that is located at an upper end of the pipe, and

A plurality of flare tips, each comprising a hollow body in fluid communication with the upper end of the riser pipe, in which one or more of the flare tips is provided with a mechanical non-return valve that is normally closed and which opens when the pressure of the gas flowing along the pipe exceeds a defined level.

All of the flare tips but one may be provided with a mechanical non-return valve that is normally closed and which opens when the pressure of the gas flowing along the pipe exceeds a defined level.

The remaining one may simply be an open ended flare tip with no valve to control the flow through the flare tip. This may have a flow rate equal to the reciprocal of the turn down ratio of the flare stack as this will be the only tip through which gas flows at the lowest turn down of the stack when all the flaps are closed.

The mechanical non-return valve may comprise a flap that is connected to the hollow body of the flare tip by a hinge, or by other means such as a simply weighted disc retained within a cage Two or more of the flare tips may each be provided with a flap that is normally closed and which opens when the pressure of the gas flowing along the pipe exceeds a defined level.

The flaps of two or more of the flare tips may each open at the same pressure of gas flowing along the pipe.

Alternatively, one of the flaps may open at a lower pressure than the other flaps.

The or each flap may be weighted to precisely control the flow pressure required to open the flap.

The flap or each flap may include a resilient biasing means, such as a spring, the force of the spring controlling the flow pressure required to open the flap.

Each flap may be configured to open when the gas flow creates a gas pressure incrementally higher than the opening set point of the previous tip flap, say 5mbar. A normal turndown ratio for a flare would be in the region of 5 : 1 , with the addition of the weighted non-return valves the range can be increased to have a turn down ratio of at least 10: 1 and preferably at least 20: 1 or perhaps 30: 1 or higher.

The stack may be sized to operate with synthetic waste gas produced by pyrolysis of waste material.

A first one of the flare outlets may be in fluid connection with the vertical pipe at a first distance, and a second one of the flare tips may be in fluid connection with the vertical pipe at a second distance that is less than the first distance.

Two or more of the flare outlets may be located at different circumferential locations around the riser pipe.

The or each flap may be connected to the flare outlet by a hinge, the flap pivoting around the hinge. When closed the or each flap may completely seal the respective hollow body of the flare outlet. The hollow body or each hollow body of the flare outlets may comprise a length of sub-pipe connected to the vertical pipe. The sub-pipe may be welded to the pipe, and may have a smaller diameter than the vertical pipe.

Alternatively, the hollow body may comprise a deformed part of the pipe. It may, perhaps, comprise an opening formed into the pipe .

There may be at least six flare outlets.

The flare stack may have a turn down ratio of N: l and the tip that does not have a flap would be sized for 1/N of the peak flow rate . The pressure drop at high flow rate may then be the cracking pressure of the next tip non-return valve.

Each of the flare tips may be provided with a respective pilot light. Alternatively, a single pilot light may be provided and the flare tips may be positioned such that for any combination of open flare tips a single pilot light is capable of lighting the gas from each open flare tip.

The flare stack may further include a non-return valve in the pipe or at the end of the pipe to prevent the flame from travelling back along the flare stack to the gas source. The flare stack may be connected at an inlet to a flare header that is connected to a source of synthetic gas from a pyrolser.

According to a second aspect the invention provides a pyrolysis system comprising in parallel at least two process lines, each process line comprising a

pyrolysis kiln having an inlet for the dried material output from the dryer and an outlet for pyrolysis gas produced in the kiln, and a diverter valve for selecting permitting the gas to flow to a first outlet or a second outlet ;

the system further comprising a flare stack according to the first aspect of the invention that receives gas from each first outlet of the diverter valves. Providing a flare stack that is shared between multiple lines is possible because of the high turn down ratio that can be achieved using the flare tips with the flaps.

There may be two, or three, or more lines.

The flare stack may have a turn down ratio of at least 30: 1 or 40: 1 or higher.

The second outlet of each diverter valve may be connected to a heat engine that burns the pyrolysis gas, the heat engine being cooled by a fluid cooling system.

The system may include at least one dryer having an inlet and an outlet and a container therebetween for containing the organic feedstock and a heater that heats the material in the container thereby to dry the material, in which the dryer comprises a network of conduits through which heated liquid is flowed. The material output from the dryer may be passed into the or each pyrolysis kiln.

There will now be described, by way of example only, one embodiment of the present invention with reference to and as illustrated in the accompanying drawings of which: Figure 1 is an overview of a pyrolysis system which incorporates an embodiment of a flare stack in accordance with an aspect of the invention;

Figure 2 is a representation of the flare stack shown in the overview of Figure 1 ; Figure 3 is a more detailed view of one of the flare tips of the flare stack of Figure 2;

Figure 4 shows an alternative embodiment of a flare stack in accordance with the invention; Figure 5 shows a further alternative embodiment of a flare stack in accordance with the invention; and

Figure 6 is a block diagram showing the use of a single flare stack with multiple pyrolysis lines. Figure 1 is an overview of the different stages of a complete pyrolysis system that includes an exemplary flare stack for burning off excess gas that is in accordance with the present invention. The reader will appreciate that various modifications to the system can be made within the scope of the present invention, and that the modified system would also fall within the scope of the present invention.

The system starts with feedstock material 1 on the left side of Figure 1 , which may be municipal source waste or refuse derived waste although other solid wastes can be used. The feedstock moves through the process from the left to the right hand side of the flow diagram, being transformed into char and gas and other materials during the process to the final output gas and energy 2 on the right hand side. The feedstock material is fed into a feedstock conditioner 3 which shreds, dries and sorts the waste before it is weighed and then compacted 4 and fed into a pyrolysis kiln 4. The compaction ensures an air tight seal is achieved at the input to the pyrolysis kiln 5. The kiln may be of the rotating drum type described in GB2441721.

The kiln is heated by combustion 5 to cause the material in the kiln to be pyrolysed, and the pyrolysed gas and carbon particulate is removed from the kiln at high temperature and fed into a filtering stage 6 which removes solids and the gas is then quenched 7 to cool the gas and remove effluents 8, heavy oils 9 and light oils 10. The cleaned gas is the fed via a diverter valve 1 1 to a heat engine 12, such as a gas turbine, which generates heat or electricity as the energy output 2. In the event that the rate of production of gas is too high for the engine 12 to consume- say if the engine is off line- the diverter valve 1 1 can send the gas to a flare 13 where it is burnt off.

The filter 6, as well as passing the solid free gas, also extracts char 14 which is collected and further gasified 15. The gas produced, together with any light oil 10 removed during quenching 7, is used as fuel to heat the combustion furnace 5 that heats the pyrolysis kiln. The hot air and exhaust from the heating of the pyrolysis chamber is recirculated to extract the heat energy in a process of regeneration 16, and the extract heat is used in turn to heat the air being fed to the furnace . This ensures that no energy is wasted. The ash produced from gasification is cooled and bagged for removal. The rate of flow of gas to the flare stack may be very variable, and to handle this a design of flare stack with a very high turn down ratio is required. Also, for safety, it is preferred that the flare stack can manually cope with all the rates of flow expected without the need to automatically open or close air inlet valves. This ensures that the flare stack will continue to operate, at least for a short time, in the event of a low of electrical power.

Figure 2 shows a flare stack 13 that falls within the scope of the present invention. The flare stack 13 comprises a tubular pipe 20, which is generally vertical and forms a riser along which gas to be burnt can flow. The riser has an inlet 32 towards the bottom and an outlet 22 at the top. The inlet at the bottom of the pipe 20 is in fluid communication with a source of synthetic gas that is to be burnt. The top of the tube is provided with a plurality of flare tips 23, each comprising a hollow body 23a that is in fluidic communication with the gas flowing out of the outlet of the tube. Note that the outlet in this example is considered to be the upper portion of the rather than the very terminal end of the riser.

There are three flare tips 23 in the example of figure 2. A first tip is formed by a narrowing of the terminal end of the riser. The other two flare tips 23 are provided on opposing sides of the riser. Each one is connected to the riser pipe 20 a short distance below the end of the riser through an elbow. As best shown in Figure 3, each flare tip 23 has an inlet end 24 where it meets the riser and an outlet end 25. The outlet end of each flare tip is provided with a flap 26 that is located by a hinge 27 along one edge. The flap 27 is normally closed and rests on top of the upper end of the flare tip. The flap is forced open when the pressure of the gas flowing along the pipe exceeds a defined level. The flare tip shown in Figure 3 comprises a small diameter sub-pipe which is covered at its end by a disc shaped flap 26. The flap 26 is connected along length of its circumference to a simple barrel type hinge, with a hinge pin that passes through a bore in both the flap and the sub-pipe wall. The flap is normally closed under its own weight, opening when the pressure of gas on the underside is sufficient to overcome the weight. The flap can be tuned to open at certain gas pressure by the addition of a weight or use of a spring, or the flap itself can simply be made to the required weight so that no additional weights are needed. Associated with each of the three flare tips in Figure 2 is a pilot light 28. This pilot light 28 is used to start a flame when gas escapes through the flare tip as the flap is forced open. A single pilot light could be shared between all three of the flare tips. In use, the inlet of the flare stack 13 is connected to an outlet of a flare header. The inlet of the flare header is connected through a manifold to the filter of the system of figure 1. In some cases, the manifold allows the flare stack to be connected to multiple filters each fed with gas from multiple pyrolysis kilns. This allows a small system to be scaled up and a single flare stack can be used because of its very good turn down ratio. When the gas flow is very low, all of the flaps will be closed and gas only escapes from the top of the riser where it is formed into a flame. As gas rises, one or both of the flaps will open to allow gas to allow escape through the two flaps where it is also burnt off. When gas escapes from these two flare tips, the rate of flow of gas through the open flare tip in the centre automatically decreases, preventing that flame from blowing itself out.

Figure 4 shows an alternative flow stack 30 that also falls within the scope of the present invention. This is the same as the stack of Figure 2, and for convenience the same reference numerals have been used to indicate like parts. However, it does differ in that the two side flare tips 23 are connected to the riser at different heights along the riser pipe.

Figure 5 shows a view from above of a still further alternative embodiment of a flare stack 40 in which a set of five flare tips 23 are provided, spaced around the central vertical pipe.

Figure 6 shows how a flare stack 13 can be shared between multiple pyrolysis lines. As shown each line comprises a pyrolysis kiln 50 that generates synthetic gas by pyrolysing feedstock. This is then fed to a filter 60 that removes ash and other contaminants, and the gas is fed to a diverter valve 70 with two outlets. One of the outlets is connected to a manifold 80 and to a flare header that is connected to the flare stack 13. This allows all of the lines to send gas to the shared flare stack.

Claims

1. A flare stack for use in burning off the gas products produced by a pyrolysis system, the flare assembly comprising:

2. A flare stack according to claim 1 in which all of the flare tips but one are provided with a mechanical non-return valve that is normally closed and which opens when the pressure of the gas flowing along the pipe exceeds a defined level.

3. A flare stack according to claim 1 or claim 2 in which the mechanical nonreturn valve comprises a flap that is connected to the hollow body of the flare tip by a hinge.

4. A flare stack according to claim 3 in which each flap is configured to open when the gas flow creates a gas pressure incrementally higher than the opening set point of the previous tip flap, say 5mbar.

5. A flare stack according to claim 3 in which the flaps of two or more of the flare tips each open at the same pressure of gas flowing along the pipe.

6. A flare stack according to any one of claims 3 to 5 in which each flap is weighted to precisely control the flow pressure required to open the flap.

7. A flare stack according to any one of claims 3 to 6 in which the flap or each flap, includes a resilient biasing means, such as a spring, the force of the spring controlling the flow pressure required to open the flap.

8. A flare stack according to any one of claims 1 to 7 having a turn down ratio of at least 30: 1.

9. A pyrolysis system comprising in parallel at least two process lines, each process line comprising a

the system further comprising a flare stack according to any one of claims 1 to 8 that receives gas from each first outlet of the diverter valves.