Assembly and method for organic sediment processing and stabilisation

Abstract

Sediment treatment assembly comprising a number of sequentially arranged devices for processing and stabilizing organic sediment, including one or more toxic or inflammable gas components and to remove larger particulate matter and water and to transfer the residual organic sediment to storage. The assembly comprises: - a degasser (3) arranged to remove gas and at least one of ventilator (5) or an enclosed flare system (6) - a mechanical separator (7) arranged to separate out coarse particles; - a first water reduction device (10); - a second water reduction device (12); - a water treatment unit (15) to process effluent water prior to its disposal.

Description

[0001] Assembly And Method For Organic Sediment Processing And Stabilisation

[0002] The present invention concerns a sediment stabilising assembly as indicated by the preamble of claim 1. According to another aspect, the invention concerns a sediment stabilising treatment method as indicated by the preamble of claim 13.

[0003] Background

[0004] In many areas around the world, the seabed is contaminated with pollutants from various sources. These pollutants are often having a negative impact on the marine life and benthic fauna. Similar conditions can be found at aquaculture farms where in some cases organic overloading results in a deteriorated condition locally affecting the benthic fauna and marine life.

[0005] Existing methods involve encapsulation of the contaminated areas or in some cases removal by dredging and subsequent collection of the material at surface. However, none of these methods are addressing the biological aspects required to stabilize these materials.

[0006] Processes and equipment for handling multiphase fluids are widely used in the drilling industry, which make use of the equipment such as degassers, shakers and cyclones, to remove gas, drill cuttings and other impurities before the mud is recycled into the bore hole. This process however does not address the biological aspects that are required to effectively process and stabilize organic sediments from seabed.

[0007] Other methods to process this type of sediments can be found in land-based fish farms or hatcheries, so called RAS (Recirculating Aquaculture System) or Flow through systems. These are systems effective to process large quantities of water containing low concentrations of sediment < 1% DM (Dry Matter) and also address the biological aspects. However, the equipment and processes used do not allow for high loads of sediment in the capacities as required for the invention.

[0008] Norwegian patent No. 345 318 (issued 2020) concerns a method and system for removal of sludge under an aquaculture plant. It is mainly concerned with the technicalities of how to extract the material from the sea floor using a free floating ROV with a suction house and a suction head. The ROV may be programmed to move in a grid-like pattern to cover the desired area. Equipment above water may include a mixing vessel, a pre-filter a band filter, a station for polymer addition and a screw press, as well as additional filters to clean the water before allowing it back to the sea. WO 2018 032833 Al teaches a treatment system for contaminated sand, comprising a garbage sorting device, which is used for garbage separation of the contaminated sand as well as a a sediment separation device for precipitating the sediment mixture to obtain recyclable residual sand separated from sludge, based on density and particle size. A washing device for washing pollutants such as heavy metals and organic matters is also included.

[0009] GB 2452071 A concerns an apparatus and method for treating sediments, such as hydrocarbon waste products of a type including intractable liquids, sludges and solids etc. comprising a hermetically sealable chamber, into which the sediment to be treated is deposited and a heat source for heating the sediment within the chamber to thereby release one or more gaseous components. The apparatus further comprises a controller arranged to monitor the conditions within the chamber so as to automatically purge the chamber when a predetermined pressure and / or gaseous content is exceeded, preferably using inert gas. The apparatus and method are particularly useful in hydrocarbon recovery processes.

[0010] Objectives

[0011] It is an objective of the present invention to provide a processing system, a device, an assembly or a method for stabilization of sediments originating from any contaminated seafloor.

[0012] The present invention

[0013] The above indicated objective is fulfilled by the assembly defined by claim 1, which represents a first aspect of the present invention. The method defined by claim 13 represents a second aspect of the present invention.

[0014] Preferred embodiments of the invention are disclosed by the dependent claims.

[0015] The present invention covers the process and associated equipment required to purify and stabilize contaminated sediment from a seabed for subsequent storage of the organic sediment and optional return to the seabed of the original matter.

[0016] During ascend to surface the gas in the sediment mixture will expand resulting in a lower density of the mixture and as such a reduction in hydrostatic pressure. A larger water depth will increase this effect.

[0017] At the treatment plant, the sediment mixture is routed to a degasser vessel. The purpose is to remove the gas from the mixture as a first step in the stabilization process. The gas leaving the degasser vessel in some cases contains hydrogen sulphide, methane and potentially ammonia. Depending on local requirements and gas composition the gas can be led over two pellet filters to remove the traces of hydrogen sulphide and ammonia from the gas stream. The remaining gas can either be vented to a safe area with sufficient quantities of air, be stored for sale or alternatively be burned in an enclosed flare system.

[0018] The mandatory steps of the treatment process include degassing, mechanical separation of larger particles, dewatering to reduce weight and volume of the resulting organic material at a comparatively high dry material content, typically in the region of at least 30 % and water treatment of disposal water.

[0019] The assembly is modular and additional process steps can be added to remove sand from the organic matter and / or to increase the dry weight content of the organic sediment in a range from 45% to 90% DM. The system configuration will be depending on the type of sediment recovered, area of operation and the local requirements.

[0020] Furthermore, the process and device include steps and devices to take care of hazardous gaseous components in the form of ammonia, methane and hydrogen sulphide.

[0021] Further details of the invention in the form of non-limiting embodiments referring to enclosed drawing.

[0022] Figure 1 is a flow diagram of an embodiment of the process according to the present invention.

[0023] The sediment mixture 1 from the seafloor enters the first step / device according to the present invention, which is a degassing vessel 3 from which the off-gas leaves as flow 21 and the solid material, including water, as flow 22, the latter entering a screen shaker 7 or the like arranged to separate out particles larger than 1 and up to 4 mm in size. The larger particles are discharged as flow 23. Residual gas 25 is typically released also in this step, and is combined with flow 21 from the degasser in an enclosed environment

[0024] The large particulate matter leaves the screen shaker as flow 23, effluent water leaves as flow 24 while the sediment mixture leaves as flow 26 and may pass through a mixing station 8 allowing polymer (not shown) to be added if desired. The resulting flow 27 then typically passes through a buffer tank 9. As an alternative, the mixing station 8 may be arranged downstream of the buffer tank 9. Residual gas 29 may leave the buffer tank 9 to be combined with gas flows 21 and 25 in an enclosed environment. A sediment flow 28 from the buffer tank 9 enters a first water reduction device 10 in the form of a belt filter or the like in which additional water is removed as flow 30. Residual gas 31 leaves this step to be combined with the above mentioned flows of off-gas.

[0025] Some or all of the sediment flow 32 from the belt filter 10 can be routed to an agitation unit such as an ultrasonic agitator 11 or a high shear mixer in combination with a cyclone separator from which sand is separated as flow 35 and typically returned to the sea floor. All or part of flow 32 may as an alternative be directed to a decanter centrifuge 12 depending on the presence and amounts of sand present in flow 32. Alternatively, the entire sediment flow 32 can be routed directly to the decanter centrifuge 12. In some embodiments, the decanter centrifuge is replaced by a screw press. The sediment leaving the decanter centrifuge (or screw press) is typically dewatered to a dry matter content up to 30% DM. Depending largely upon a cost / benefit, a thermal drying unit 14 can be included in the assembly to achieve higher dry matter contents from 45% up to 90% DM.

[0026] All or some of the effluent water can be routed through a water treatment unit 15. Typical treatment in this system involves the removal of particulate matter up to 50 micron and sterilisation of marine organism and pathogens by means of UV light. Some of the water can be discharged to sea directly as flow 40, not being directed though the water treatment unit depending upon presence of pathogens and organisms.

[0027] The gas flow may be routed through a series of pellet filters 4 to isolate harmful components such as ammonia (NH3) and / or hydrogen sulphide (H?S). From the pallet filters the gas can either be vented off by means of forced ventilation or alternatively is burned in a flare system 6. The configuration will be depending on the gas composition, area of operation and local requirements. The pellet filters (module 4) are included if levels of ammonia and hydrogen sulphide would cause problems while performing the operation in urban areas (for example). The flare system 6 is typically included if amounts of methane are such that burning this on site is the most efficient way of processing. The flare system is typically included when significant amounts of methane (natural gas) is present and released in the degasser.

Claims

Claims1. Sediment treatment assembly comprising a number of sequentially arranged devices for processing and stabilizing organic sediment, including one or more toxic or inflammable gas components and to remove larger particulate matter and water and to transfer the residual organic sediment to storage under or above water, characterized in and comprising in sequence- a degasser (3) arranged to remove gas and at least one of ventilator (5) or an enclosed flare system (6)- a mechanical separator (7) arranged to separate out coarse particles;- a first water reduction device (10);- a second water reduction device (12);- a water treatment unit (15) to process effluent water prior to disposal.

2. Sediment treatment assembly as claimed in claim 1, further comprising a filter unit (4), preferably comprising pellet filters in series, arranged to isolate at least some of the different gas components discharged from the degasser (3).

3. Sediment treatment assembly as claimed in any one of the preceding claims, wherein the mechanical separator (7) is selected from the group consisting of screen shaker, or rotating filter belts.

4. Sediment treatment assembly as claimed in any one of the preceding claims, wherein the mechanical separator (7) is arranged to separate out particles of diameter larger than a size adjustable from 1 to 4 mm.

5. Sediment treatment assembly as claimed in any one of the preceding claims, wherein a mixing station (8) allowing polymer addition is arranged upstream of the first water reduction device (10).

6. Sediment treatment assembly as claimed in any one of the preceding claims, wherein the first water reduction device (10) is a belt filter device.

7. Sediment treatment assembly as claimed in any one of the preceding claims, wherein the second water reduction device (12) is a decanter centrifuge or a screw press.

8. Sediment treatment assembly as claimed in any one of the preceding claims, further comprising a buffer tank (9) arranged to receive sediment mixture from at least one of the mechanical separator (7) and the mixing station (8).

9. Sediment treatment assembly as claimed in any one of the preceding claims, wherein the first water reduction device (10) is arranged to increase the dry matter content to at least 12 % by weight, preferably at least 15 %.

10. Sediment treatment assembly as claimed in any one of the preceding claims, further comprising, downstream of the first dewatering device (10), an agitation unit (11) selected from the group consisting of ultrasonic agitation units or high shear mixing units, optionally in combination with a cyclone separator.

11. Sediment treatment assembly as claimed in any one of the preceding claims, further comprising a thermal drying station (14) downstream of all above mentioned units and devices.

12. Sediment treatment assembly as claimed in any one of the preceding claims, wherein the water treatment unit (15) is arranged to purify the effluent water from one or more units and devices of the assembly by at least one of removal of particulate matter up to 50 micron and sterilisation of marine organism and pathogens by means of UV light.

13. Sediment treatment method comprising a number of sequentially arranged steps for processing and stabilization of organic sediment, including one or more toxic or inflammable gas components and to remove larger particulate matter and water and to transfer the resulting to a sediment storage under or above water, characterized in comprising in sequence- subjecting the sediment to degassing to release gas components;- mechanically separating out coarse particles;- agitating the remaining sediment to separate out sand, providing a sand-reduced organic sediment;- subjecting the sand-reduced organic sediment to water reduction,- transferring the treated organic sediment to the sediment storage.

14. Sediment treatment method as claimed in claim 13, further comprising isolating at least some of the released gas components.

15. Sediment treatment method as claimed in claim 14, further comprising burning inflammable gas components.

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