The present invention relates to hydrothermal liquefaction (HTL) reactors for converting a feedstock containing carbon into a product comprising a bio-oil. The present invention also extends to methods for converting a feedstock containing carbon into a product comprising a bio-oil.

Hydrothermal liquefaction (HTL) is a process for converting biomass, or another carbon-containing material, and water to bio-oil, bio-char and organic gas fractions. The process is conducted at high pressures and at temperatures of between 250°C and 350°C, in the absence of oxygen. Currently, the heat to initiate HTL is supplied either by combustion of fuels, waste industrial heat or electricity. Provision of heat using such methods is problematic because the energy return on the creation of new bio-oil is too costly both energetically and economically. Additionally, the net gain in energy provision comes at the expense of the pre-combustion of other fuels, negating the formation of a renewable form of bio-oil.

Berberoglu et al. (2013) describes how solar thermal heat may be supplied to a heat transfer liquid. This heat can then be translocated to an adjacent reactor site to power a HTL process. However, this process of obtaining heat from solar energy and then transferring it to an adjacent reactor is inefficient.

Pearce et al. 2015 describes how instead of having the solar reactor and receiver as separate entities to the HTL reactor, they can be integrated. Such solar receiver HTL reactors could be sited in the thermal focal point of a concentrated solar power (CSP) parabolic trough. However, there are volumetric constraints on the physical size of such thermal focal points. These are determined by various criteria including the orientation of CSP mirrors, the shape and aperture of CSP troughs and the material properties and dimensions of solar receivers. The HTL reactors described by Pearce et al. are costly to build. Accordingly, to be commercially viable they would need to have a high volumetric and/ or throughput capacity. However, the reactors described by Pearce et al. have a small volumetric capacity and a low throughput. The present invention arises from the inventor's work in trying to overcome the problems associated with the prior art. In accordance with a first aspect of the invention, there is provided a hydrothermal liquefaction (HTL) reactor comprising:

at least one processing conduit configured to receive a feedstock comprising carbon, and to maintain the feedstock therein at an increased temperature and pressure during a hydrothermal liquefaction reaction, to thereby convert the feedstock into a product comprising a bio-oil; and

a heat exchange conduit disposed at least substantially adjacent to the at least one processing conduit, and configured to receive a coolant therein to reduce the temperature of the product disposed in the at least one processing conduit.

Advantageously, the heat exchange conduit is arranged to rapidly cool the temperature of the bio-oil product once the HTL reaction has occurred, thereby reducing the processing time and increasing the throughput of the HTL reactor.

It maybe appreciated that bio-oil is sometimes referred to as "bio-crude" and is a crude-like oil. Bio-oil typically has a lower heating value of 33.8-36.9 MJ/kg and 5-20 wt% oxygen.

Preferably, the HTL reactor comprises a feedstock inlet conduit configured to transport the feedstock to the at least one processing conduit. Preferably, the HTL reactor comprises a product outlet conduit configured to transport the product from the at least one processing conduit.

Preferably, the HTL reactor comprises a heat exchange inlet conduit configured to transport the coolant to the heat exchange conduit. Preferably, the HTL reactor comprises a heat exchange outlet conduit configured to transport the coolant from the heat exchange conduit. Preferably, the heat exchange inlet conduit is disposed substantially adjacent to the product outlet conduit. Preferably, the heat exchange outlet conduit is disposed substantially adjacent to the feedstock inlet conduit.

Advantageously, in use heat will be transferred from the product to the coolant. The heated coolant will then pass adjacent to feedstock disposed in the feedstock inlet conduit and heat will be transferred from the coolant to the feedstock, thereby preheating feedstock prior to the next reaction cycle. Preferably, the HTL reactor comprises a feedstock pump configured to transport the feedstock from a feedstock store to the at least one processing conduit. Preferably, the feedstock pump is configured to transport the feedstock from a feedstock store, through the feedstock inlet conduit, to the at least one processing conduit. Preferably, the feedstock pump is further configured to transport the product from at least one processing conduit to the product outlet conduit.

Preferably, the HTL reactor comprises a coolant pump configured to transport the coolant from a coolant store to the heat exchange conduit. Preferably, the coolant pump is configured to transport the coolant from the coolant store, through the heat exchange inlet conduit, to the heat exchange conduit. Preferably, the coolant pump is further configured to transport the coolant from the heat exchange conduit to the heat exchange outlet conduit. The heat exchange conduit may comprise a heat tolerant, conducting material. The heat exchange conduit may comprise a metal or metal alloy. The metal or metal alloy may comprise steel, copper, aluminium and/or titanium. The steel may comprise stainless steel and/or austenitic steel, and preferably comprises austenitic stainless steel.

The heat exchange conduit may comprise a wall defining an internal surface and an external surface. The wall may have a thickness of at least o.ooi mm, preferably at least 0.005 rnm, more preferably at least o.oi mm or at least 0.05 mm, and most preferably at least 0.1 mm. The wall may have a thickness of less than 100 mm, preferably less than 50 mm, more preferably less than 10 mm or less than 5 mm, and most preferably less than 3 mm. The wall thickness may be between 0.001 mm and 100 mm, preferably between 0.005 mm and 50 mm, more preferably between 0.01 mm and 10 mm or between 0.05 mm and 5 mm, and most preferably between 0.1mm and 3mm. Preferably, the internal surface of the heat exchange conduit is black, more preferably matt black, preferably painted matt black. Preferably, the external surface of the heat exchange conduit is black, more preferably matt black, preferably painted matt black. Advantageously, the black colour enhances the conductive properties of the heat exchange conduit. Preferably, the heat exchange conduit extends in a substantially longitudinal direction between the heat exchange inlet conduit and the heat exchange outlet conduit.

Preferably, the heat exchange conduit extends substantially along the longitudinal axis of the HTL reactor. Preferably, the heat exchange conduit is substantially centrally aligned in the reactor, more preferably with one or more processing conduit disposed therearound.

Preferably, the at least one processing conduit extends in a substantially longitudinal direction between a feedstock inlet and a product outlet. Preferably, the heat exchange conduit extends substantially parallel to the at least one processing conduit. Preferably, the at least one processing unit is radially disposed outside of the heat exchange conduit.

The coolant may comprise a fluid, preferably a liquid or a gas. Preferably, the coolant comprises a liquid. Preferably, the coolant comprises water, mineral oil, ethylene glycol, propylene glycol, 1,3 propandiol, caster oil and/ or liquid nitrogen. The water preferably comprises de-ionised water. The coolant may also comprise a corrosion inhibitor. The corrosion inhibitor may comprise a nitrogen containing organic compound, such as an amine, an amide, a quaternary ammonium salt, and/or a surfactant based imidazoline compound. Advantageously, corrosion inhibitors affect the critical micelle concentration or surfactant agglomeration properties and electrostatic attractive ionic charge between the inhibitor molecule and the metal surface in response to changes in temperature, pressure and interfacial free energies. In one embodiment, the at least one processing conduit consists of one processing conduit. However, in a preferred embodiment, the reactor comprises a plurality of processing conduits. Advantageously, the large surface area of the plurality of processing conduits further reduces the time required to cool the temperature of the bio-oil product once the HTL reaction has occurred, thereby further reducing the processing time and increasing the throughput of the HTL reactor.

Preferably, the reactor comprises at least 2, at least 3, at least 4 or at least 5 processing conduits, more preferably at least 10, at least 15, at least 20 or at least 25 processing conduits, and most preferably at least 30 processing conduits. Preferably, the reactor comprises less than 200, less than 150, less than 125 or less than 100 processing conduits, more preferably less than 90, less than 80, less than 70 or less than 60 processing conduits, and most preferably less than 50 processing conduits.

Preferably, each of the processing conduits extends between the feedstock inlet and the product outlet substantially parallel to each other. Preferably, a plurality of the processing conduits creates an array disposed around the outer surface of the heat exchange conduit. Preferably, the array is ordered and substantially non-random.

Preferably, the processing conduits are disposed in defined rows or layers around the central heat exchange conduit. Accordingly, the processing conduits may be disposed in 1, 2, 3, 4, 5, 6 or 7 defined rows or layers around the central heat exchange conduit. Preferably, the processing conduits may be disposed in 2, 3 or 4 defined rows or layers around the central heat exchange conduit.

In a preferred embodiment, the HTL reactor substantially possesses rotational symmetry around a central axis. Advantageously, such symmetry means that heat distribution will be uniform.

For instance, in one embodiment, the reactor comprises 48 processing conduits arranged in three layers, where an internal layer consists of 12 processing conduits, an intermediate layer consists of 16 processing conduits and an external layer consists of 20 processing conduits.

Preferably, the or each processing conduit has an external diameter of at least 0.1 mm, more preferably at least 0.5 mm, at least 1 mm, at least 1.5 mm or at least 2 mm, and most preferably at least 3 mm, at least 4 mm, at least 5mm, at least 6 mm, at least 7 mm, at least 8 mm, at least 9 mm or at least 10mm. Preferably, the or each processing conduit has an external diameter of less than 50 mm, more preferably less than 40 mm, less than 35 mm, less than 30 mm or less than 25 mm, and most preferably less than 20 mm, less than 19 mm, less than 18mm, less than 17 mm, less than 16 mm, less than 15 mm, less than 14 mm or less than 13mm. Preferably, the or each processing conduit has an external diameter of between 0.1 mm and 50 mm, more preferably between 0.5 mm and 40 mm, between 1 mm and 35 mm, between 1.5 mm and 30 mm or between 2 mm and 25 mm, and most preferably between 3 mm and 20 mm, between 4 mm and 19 mm, between 5mm and 18 mm, between 6 mm and 17 mm, between 7 mm and 16 mm, between 8 mm and 15 mm, between 9 mm and 14 mm or between 10mm and 13 mm. Advantageously, a processing conduit having a diameter in the ranges described herein are large enough to prevent char build up but small enough to ensure that the temperature therein may be rapidly reduced when the coolant is fed into the heat exchange conduit.

Preferably, the cross-section area of all of the processing conduits combined is at least ι cms, more preferably at least 5 cms, _a t least 10 cms, _a t least 15 cms, ₀ r at least 20 cms, and most preferably at least 25 cms, _a t least 30 cms, _a t least 35 cms, _a least 40 cms, _a least 45 cms, ₀ r at least 50 cms. Preferably, the cross-section area of all of the processing conduits combined is less than 500 cms, more preferably less than 400 cms, less than 300 cms, less than 200 cms, ₀ r less than 100 cms, _an d most preferably less than 95 cms, less than 90 cms, less than 85 cms, less than 80 cms, less than 75 cms, ₀ r less than 70 cms. Preferably, the cross-section area of all of the processing conduits combined is between 1 cms _an d 500 cms, more preferably between 5 cms _an d 00 cms, between 10 cms _an d 300 cms, between 15 cms _an d 200 cms, ₀ r between 20 cms _an d 100 cms, _an d most preferably between 25 cms _an d 95 cms, between 30 cms _an d 90 cms, between 35 cms _an d 85 cms, between 40 cms _an d 80 cms, between 45 cms _an d 75 cms, or between 50 cms _an d 70 cms. Preferably, the at least one processing conduit is configured to maintain the feedstock therein at a temperature of at least 50°C, more preferably at a temperature of at least ioo°C, at least 150°C or at least 200°C, and most preferably at a temperature of at least 250°C. Preferably, the at least one processing conduit is configured to maintain the feedstock therein at a temperature of less than 550°C, more preferably at a temperature of less than 500°C, less than 450°C or less than 400°C, and most preferably at a temperature of less than 350°C. Preferably, the at least one processing conduit is configured to maintain the feedstock therein at a temperature of between 50°C and 550°C, more preferably at a temperature of between ioo°C and 500°C, between 150°C and 450°C, or between 200°C and 400°C, and most preferably at a temperature of between 250°C and 350°C.

Preferably, the at least one processing conduit is configured to maintain the feedstock therein at a pressure of at least 5 MPa, more preferably at a pressure of at least 7.5 MPa, at least 10 MPa or at least 12.5 MPa, and most preferably at a pressure of at least 15 MPa. Preferably, the at least one processing conduit is configured to maintain the feedstock therein at a pressure of less than 50 MPa, more preferably at a pressure of less than 40 MPa, less than 30 MPa or less than 25 MPa, and most preferably at a pressure of less than 20 MPa. Preferably, the at least one processing conduit is configured to maintain the feedstock therein at a pressure of between 5 MPa and 50 MPa, more preferably at a pressure of between 7.5 MPa and 40 MPa, between 10 MPa and 30 MPa, or between 12.5 MPa and 25 MPa, and most preferably at a pressure of between 15 MPa and 20 MPa.

The at least one processing conduit may comprise stainless steel, preferably pressure- resistant stainless steel. The stainless steel may have a thickness of at least 0.005 mm, preferably at least 0.01 mm, more preferably at least 0.05 mm or at least 0.1 mm, and most preferably at least 0.5 mm. The stainless steel may have a thickness of less than 100 mm, preferably less than 50 mm, more preferably less than 10 mm or less than 5 mm, and most preferably less than 3.5 mm. The stainless steel may have a thickness e between 0.005 ^mm and 100 mm, preferably between 0.01 mm and 50 mm, more preferably between 0.05 mm and 10 mm or between 0.1 mm and 5 mm, and most preferably between 0.5 mm and 3.5 mm.

An internal surface of the at least one processing conduit may comprise an anti- corrosion substance. Additionally, an external surface of the at least one processing conduit may comprise an anti-corrosion substance. The anti-corrosion substance may comprise a ceramic layer. The ceramic layer may comprise aluminium oxide (Al ₂ 0 ₃ ) and/or titanium dioxide (Ti0 ₂ ). Preferably, the ceramic layer comprises aluminium oxide (AI2O ₃ ) and titanium dioxide (Ti0 ₂ ). In a most preferred embodiment, the ceramic layer comprises 60% (w/w) aluminium oxide (Al ₂ 0 ₃ ) and 40% (w/w) titanium dioxide. Alternatively, or additionally, the anti-corrosion substance may comprise nickel, molybdenum, a zinc alloy and/or polytetrafluoroethylene (PTFE).

Preferably, the HTL reactor comprises a feedstock inlet valve configured to control the flow of feedstock from the feedstock inlet conduit into the at least one processing conduit. The HTL reactor may comprise a plurality of feedstock inlet valves, wherein a feedstock inlet valve is disposed in each of the plurality of the processing conduits. Preferably, each feedstock inlet valve is disposed substantially adjacent to the feedstock inlet conduit. However, in a preferred embodiment, the HTL reactor comprises a feedstock inlet valve disposed in the feedstock inlet conduit. Preferably, the feedstock inlet valve is disposed substantially adjacent to the at least one processing conduit. Preferably, the HTL reactor comprises a product outlet valve configured to control the flow of product from the at least one processing conduit into the product outlet conduit. The HTL reactor may comprise a plurality of product outlet valves, wherein a product outlet valve is disposed in each of the plurality of the processing conduits. Preferably, each product outlet valve is disposed substantially adjacent to the product outlet conduit.

However, in a preferred embodiment, the HTL reactor comprises a product outlet valve disposed in the product outlet conduit. Preferably, the product outlet valve is disposed substantially adjacent to the at least one processing conduit.

The feedstock inlet valve preferably comprises a pressure relief valve and is configured to discharge feedstock and/or product from the at least one processing conduit into the feedstock inlet conduit if the pressure in the at least one processing conduit rises above a predetermined pressure. The product outlet valve preferably comprises a pressure relief valve and is configured to discharge feedstock and/ or product from the at least one processing conduit into the product outlet conduit if the pressure in the at least one processing conduit rises above a predetermined pressure. The predetermined pressure may be at least 20 MPa, more preferably at least 25 MPa, at least 30 MPa or at least 40 MPa, and most preferably at least 50 MPa.

The heat exchange conduit may be disposed surrounding the at least one processing conduit. In one embodiment, the at least one processing conduit may be disposed within the heat exchange conduit. In this embodiment, the coolant preferably comprises water. Advantageously, the heat exchange conduit acts as an insulator to prevent thermal losses due to external air circulation.

However, in a preferred embodiment, the at least one processing conduit is disposed surrounding the heat exchange conduit. Preferably, the heat exchange conduit has an external diameter of at least 1 mm, preferably at least 2 mm, at least 3 mm, at least 4 mm or at least 5 mm, more preferably at least 10 mm, at least 15 mm or at least 20 mm, and most preferably at least 35 mm, at least 40 mm, at least 45 mm or at least 50 mm. The heat exchange conduit may have an external diameter of less than 250 mm, preferably less than 200 mm, less than 175 mm, less than 150 mm or less than 125 mm, more preferably less than 100 mm, less than 95mm or less than 90 mm, and most preferably less than 85 mm, less than 80 mm, less than 75 mm or less than 70 mm. The heat exchange conduit may have an external diameter of between 1 mm and 250 mm, preferably between 2 mm and 200 mm, between 3 mm and 175 mm, between 4 mm and 150 mm or between 5 mm and 125 mm, more preferably between 10 mm and 100 mm, between 15 mm and 95 mm or between 20 mm and 90 mm, and most preferably between 35 mm and 85 mm, between 40 mm and 80 mm, between 45 mm and 75 mm or between 50 mm and 70 mm.

Preferably, the HTL reactor comprises a coolant valve configured to control the flow of coolant through the coolant conduit. The coolant valve may be disposed in the heat exchange inlet conduit, the heat exchange conduit and/ or the heat exchange outlet conduit. In a preferred embodiment, the coolant valve is disposed in the heat exchange inlet conduit substantially adjacent to the heat exchange conduit. Preferably, the coolant valve is a flow control valve.

Preferably, the feedstock comprises a fluid, preferably a liquid. The liquid may comprise water and/or alcohol. The water may comprise freshwater, wastewater or seawater. The alcohol may comprise ethanol. Preferably, the feedstock comprises a solution or suspension of carbon in the fluid. The carbon may be biotic or abiotic. Most preferably, the carbon is provided as a plurality of micro-organisms or biomass. The biomass may comprise algae, microalgae, macroalgae, sewage waste, plastic waste, cellulosic waste, pectin, alginate, terrestrial- and/or marine-derived polysaccharides.

Preferably, the feedstock comprises at least 1% (w/v) biomass. More preferably, the feedstock comprises at least 5% (w/v), 10% (w/v) or 15% (w/v) biomass. Most preferably, the feedstock comprises at least 20% (w/v) biomass. Advantageously, higher concentrations of biomass increase the product yield. Preferably, the feedstock comprises less than 80% (w/v) biomass. More preferably, the feedstock comprises less than 65% (w/v) or 50% (w/v) biomass. Most preferably, the feedstock comprises less than 40% (w/v) biomass. Advantageously, lower concentrations of biomass reduce the dewatering costs. Preferably, the feedstock comprises between 1% (w/v) and 80% (w/v) biomass. More preferably, the feedstock comprises between 5% (w/v) and 65% (w/v) or between 10% (w/v) and 50% (w/v) biomass. Most preferably, the feedstock comprises between 20% (w/v) and 40% (w/v) biomass. Advantageously, a concentration of about 20% (w/v) biomass is estimated to be a good compromise between the product yield and while still providing a feedstock which it is possible to pump.

The feedstock may comprise a catalyst. The catalyst may comprise sodium carbonate. The feedstock may comprise less than 5% (w/v) catalyst. More preferably, the feedstock comprises less than 1% (w/v), 0.75% (w/v), 0.5% (w/v) or 0.25% (w/v) catalyst. Most preferably, the feedstock comprises less than 0.1% (w/v) catalyst.

Preferably, the product also comprises bio-char and/or organic gas fractions. Preferably, the HTL reactor comprises an insulator disposed around the at least one processing conduit and the heat exchange conduit. Advantageously, the insulator prevents the loss of heat from the processing conduits into the atmosphere.

In one embodiment, the HTL reactor comprises an outer conduit disposed around the at least one processing conduit and the heat exchange conduit. The outer conduit may contain a vacuum or a fluid. The fluid may comprise a gas, such as air.

Advantageously, the outer conduit is an insulator.

Preferably, the insulator has a thickness of between 0.1 mm and 100mm or between 0.5 mm and 50 mm, more preferably between 1 mm and 40 mm, between 2mm and 35 mm, between 3 mm and 30 mm, between 4mm and 25 mm, most preferably between 5 mm and 20 mm.

Preferably, the outer conduit extends in a substantially longitudinal direction between the feedstock inlet and the product outlet. Preferably, the outer conduit extends substantially parallel to the at least one processing conduit. Preferably, the outer conduit extends substantially parallel to the heat exchange conduit.

Preferably, the outer conduit has a substantially annulus or ring shaped cross-section. Preferably, the outer conduit has an external diameter of at least 10 mm, at least 20 mm, at least 30 mm or at least 40 mm, more preferably at least 50 mm, at least 60 mm, at least 70 mm, at least 80 mm or at least 90 mm, most preferably at least 100 mm. Preferably, the outer conduit has an external diameter of less than 400 mm, less than 350 mm, less than 300 mm or less than 250 mm, more preferably less than 200 mm, less than 190 mm, less than 180 mm, less than 170 mm or less than 160 mm, most preferably less than 150 mm. Preferably, the outer conduit has an external diameter of between 10 mm and 400 mm, between 20 mm and 350 mm, between 30 mm and 300 mm or between 40 mm and 250 mm, more preferably between 50 mm and 200 mm, between 60 mm and 190 mm, between 70 mm and 180 mm, between 80 mm and 170 mm or between 90 mm and 160 mm, most preferably between 100 mm and 150 mm.

Preferably, the outer conduit has an internal diameter of at least 5 mm, at least 10 mm, at least 20 mm or at least 30 mm, more preferably at least 40 mm, at least 50 mm, at least 60 mm, at least 70 mm or at least 80 mm, most preferably at least 90 mm.

Preferably, the outer conduit has an external diameter of less than 395 mm, less than 345 mm, less than 295 mm or less than 245 mm, more preferably less than 195 mm, less than 185 mm, less than 175 mm, less than 165 mm or less than 155 mm, most preferably less than 145 mm. Preferably, the outer conduit has an external diameter of between 5 mm and 395 mm, between 10 mm and 345 mm, between 20 mm and 295 mm or between 30 mm and 245 mm, more preferably between 40 mm and 195 mm, between 50 mm and 185 mm, between 60 mm and 175 mm, between 70 mm and 165 mm or between 80 mm and 155 mm, most preferably between 90 mm and 145 mm.

Preferably, the outer conduit comprises an external wall and an internal wall defining a space therebetween. Preferably, the external and internal walls are separated by a thickness of between 0.1 mm and 100mm or between 0.5 mm and 50 mm, more preferably between 1 mm and 40 mm, between 2mm and 35 mm, between 3 mm and 30 mm, between 4mm and 25 mm, most preferably between 5 mm and 20 mm.

Preferably, the internal wall is disposed substantially adjacent to the at least one processing conduit. Preferably, the space comprises the vacuum or fluid.

Preferably, the external wall comprises an insulating material, such as insulated glass or polycarbonate envelope. The external wall may have a thickness of at least 0.1 mm, preferably at least 0.5 mm, more preferably at least 1 mm or at least 3 mm, and most preferably at least 5 mm. The external wall may have a thickness of less than 100 mm, preferably less than 50 mm, more preferably less than 40 mm or less than 30 mm, and most preferably less than 20 mm. The external wall thickness may be between 0.1 mm and loo mm, preferably between 0.5 mm and 50 mm, more preferably between 1 mm and 40 mm or between 3 mm and 30 mm, and most preferably between 5 mm and 20 mm. Preferably, the internal wall comprises a heat tolerant, conducting material. The internal wall may comprise a metal or metal alloy. The internal wall may comprise steel, copper, aluminium and/ or titanium. The steel may comprise stainless steel and/or austenitic steel, and preferably comprises austenitic stainless steel. The internal wall may have a thickness of at least 0.0005 mm, preferably at least 0.001 mm, more preferably at least 0.005 rnm or at least 0.01 mm, and most preferably at least 0.05 mm. The internal wall may have a thickness of less than 100 mm, preferably less than 50 mm, more preferably less than 10 mm or less than 5 mm, and most preferably less than 2 mm. The internal wall thickness may be between 0.005 ^mm and 100 mm, preferably between 0.001 mm and 50 mm, more preferably between 0.005 mm and 10 mm or between 0.01 mm and 5 mm, and most preferably between 0.05 mm and 2 mm. Preferably, an internal surface of the internal wall is black, preferably matt black, and most preferably painted matt black. Preferably, an external surface of the internal wall is black, preferably matt black, and most preferably painted matt black.

Preferably, the HTL reactor comprises a solar receiver HTL reactor. Accordingly, the HTL reactor may comprise a solar collector. The solar collector may comprise a concentrated solar power (CSP) parabolic trough defining a focal line. The at least one processing conduit may be disposed substantially adjacent to the focal line. The or each processing conduit may extend substantially parallel to the focal line between the feedstock inlet conduit and the product outlet conduit. In the embodiment where the HTL reactor comprises a plurality of processing conduits, the plurality of the processing conduits preferably create an array disposed around the focal line. Preferably, the array is ordered and substantially non-random. Preferably, the processing conduits are disposed in defined rows or layers around the focal line.

The heat exchange conduit may be disposed substantially adjacent to the focal line. In a preferred embodiment, the heat exchange conduit is disposed on the focal line. The heat exchange conduit may extend substantially parallel to the focal line between the heat exchange inlet conduit and the heat exchange outlet conduit. Advantageously, this provides a low cost source of renewable energy for heating the feedstock to the required temperature.

Preferably, the apparatus comprises control means configured to switch the apparatus between a heating mode and a cooling mode. Preferably, the control means is configured to send a signal, which is preferably a digital signal, to the solar collector to thereby adjust the position of the solar collector to increase solar influx and

corresponding heat gain and thereby switch the apparatus to the heating mode. Preferably, the control means is configured to send an opening signal, which is preferably a digital signal, to the feedstock inlet valve and the product outlet valve to thereby open the feedstock inlet and product outlet valves and to thereby allow the flow of feedstock into the at least one processing conduit. The control means may be configured to send the opening signal to the feedstock inlet and product outlet valves before, simultaneously to, or after sending the signal to the solar collector.

Preferably, the control means is configured to send an activating signal, which is preferably a digital signal, to a feedstock pump to turn the feedstock pump to an activated mode and to thereby cause the pump to transport the feedstock from the feedstock store to the at least one processing conduit. Preferably, the control means is configured to send the activating signal to the feedstock pump simultaneously to or after sending the opening signal to the feedstock inlet and product outlet valves.

Advantageously, as feedstock is transported into the at least one processing conduit, product from a previous reaction cycle may be pumped from the at least one processing conduit and collected.

Preferably, the control means is configured to send a deactivating signal, which is preferably a digital signal, to a feedstock pump to turn the feedstock pump to a deactivated mode and to thereby stop the transport of feedstock from the feedstock store to the at least one processing conduit. Preferably, the control means is configured to send the deactivating signal to the feedstock pump a suitable time after sending the activating signal. It will be appreciated that the suitable time will vary depending on a number of factors including the size of the HTL reactor and the speed that the feedstock is transported. A suitable time will have elapsed when the at least one processing conduits comprise a sufficient amount of feedstock, e.g. the at least one processing conduits may be substantially full of feedstock.

Preferably, the control means is configured to send a closing signal, which is preferably a digital signal, to the feedstock inlet valve and the product outlet valve to thereby close the feedstock inlet and product outlet valves and to thereby prevent the flow of feedstock into or out of the at least one processing conduit. Preferably, the control means is configured to send the closing signal to the feedstock inlet and product outlet valves simultaneously to or after sending the deactivating signal to the feedstock pump.

The HTL reactor may comprise one or more temperature sensors configured to monitor the temperature in the at least one processing conduits. The temperature sensors may comprise thermometers or thermocouples. The HTL reactor may comprise one or more pressure sensors configured to monitor the pressure in the at least one processing conduits. The control means may be configured to monitor the temperature and pressure in the at least one processing conduit during the heating mode.

After a suitable time has passed, the control means is preferably configured to switch the apparatus to the cooling mode. It will be appreciated that the suitable time may vary depending upon a variety of factors.

The control means may be configured to determine when a suitable time has passed. The suitable time may be at least 1 minute after the feedstock in the at least one processing conduit reaches an elevated temperature and/or pressure, more preferably at least 5 minutes or at least 10 minutes after the feedstock in the at least one processing conduit reaches an elevated temperature and/ or pressure, and most preferably at least 15 minutes after the feedstock in the at least one processing conduit reaches an elevated temperature and/ or pressure. Preferably, the suitable time is less than 120 minutes after the feedstock in the at least one processing conduit reaches an elevated temperature and/ or pressure, more preferably less than 60 minutes or less than 45 minutes after the feedstock in the at least one processing conduit reaches an elevated temperature and/or pressure, and most preferably less than 30 minutes after the feedstock in the at least one processing conduit reaches an elevated temperature and/ or pressure. Preferably, the suitable time is between 1 minute and 120 minutes after the feedstock in the at least one processing conduit reaches an elevated

temperature and/or pressure, more preferably between 5 minutes and 60 minutes or between 10 minutes and 45 minutes after the feedstock in the at least one processing conduit reaches an elevated temperature and/or pressure, and most preferably between 15 minutes and 30 minutes after the feedstock in the at least one processing conduit reaches an elevated temperature and/ or pressure.

Preferably, the elevated temperature is at least 50°C, more preferably at least ioo°C, 150°C or 200°C, and most preferably at least 250°C. Preferably, the elevated temperature is less than 550°C, more preferably less than 500°C, 450°C or 400°C, and most preferably less than 350°C. Preferably, the elevated temperature is between 50°C and 550°C, more preferably between ioo°C and 500°C, between 150°C and 450°C, or between 200°C and 400°C, and most preferably between 250°C and 350°C.

Preferably, the elevated pressure is at least 5 MPa, more preferably at least 7.5 MPa, at least 10 MPa or at least 12.5 MPa, most preferably at least 15 MPa. Preferably, the elevated pressure is less than 50 MPa, more preferably less than 40 MPa, less than 30 MPa or less than 25 MPa, and most preferably less than 20 MPa. Preferably, the elevated temperature is between 5 MPa and 50 MPa, more preferably between 7.5 MPa and 40 MPa, between 10 MPa and 30 MPa, or between 12.5 MPa and 25 MPa, and most preferably between 15 MPa and 20 MPa.

Preferably, the control means is configured to send a signal, which is preferably a digital signal, to the solar collector, to thereby adjust the position of the solar collector to decrease solar influx, and thereby switch the apparatus to the cooling mode. Preferably, the control means is configured to send an opening signal, which is preferably a digital signal, to the coolant valve to thereby open the coolant valve and to thereby allow the flow of coolant along the at least one processing conduit. The control means may be configured to send the opening signal to the coolant valve before, simultaneously to, or after sending the signal to the solar collector. Preferably, the control means is configured to send the opening signal to the coolant valve after sending the signal to the solar collector.

Preferably, the control means is configured to send an activating signal, which is preferably a digital signal, to a coolant pump to turn the coolant pump to an activated mode and to thereby cause the coolant pump to transport the coolant from the coolant store to the heat exchange conduit. Preferably, the control means is configured to send the activating signal to the coolant pump simultaneously to or after sending the opening signal to the coolant valve.

Preferably, the control means is configured to send a deactivating signal, which is preferably a digital signal, to the coolant pump to turn the coolant pump to a deactivated mode and to thereby stop the transport of coolant from the coolant store to the heat exchange conduit. Preferably, the control means is configured to send the deactivating signal to the coolant pump a suitable time after sending the activating signal. It will be appreciated that the suitable time will vary depending on a number of factors. A suitable time will have elapsed when the temperature of the at least one processing conduit has dropped a sufficient amount. Accordingly, the control means may be configured to send the deactivating signal to the coolant pump when the one or more temperature sensors detect a temperature below a pre-determined temperature. The pre-determined temperature is preferably less than 250°C, more preferably less than 200°C, less than i8o°C, less than i6o°C, less than 140°C or less than 120°C, most preferably less than ioo°C, less than 90°C or less than 8o°C. Preferably, determined temperature is preferably between 30°C and 250°C, more preferably between 35°C and 200°C, between 40°C and i8o°C, between 45°C and i6o°C, between 50°C and 140°C or between 55°C and 120°C, most preferably between 6o°C and ioo°C, between 65°C and 90°C or between 70°C and 8o°C.

The inventor believes that the method of producing a bio-oil is also novel. Thus, in accordance with a second aspect, there is provided a method of producing a bio-oil, the method comprising:

feeding a feedstock comprising carbon into at least one processing conduit, and maintaining the feedstock therein at an elevated temperature and pressure to induce a hydrothermal liquefaction reaction, to thereby convert the feedstock into a product comprising a bio-oil; and

feeding a coolant into a heat exchange conduit, disposed at least substantially adjacent to the at least one processing conduit, to reduce the temperature of the product disposed in the at least one processing conduit. Preferably, the method of the second aspect is conducted using the HTL reactor of the first aspect. Preferably, the elevated temperature is at least 50°C, more preferably at least ioo°C, 150°C or 200°C, and most preferably at least 250°C. Preferably, the elevated temperature is less than 550°C, more preferably less than 500°C, 450°C or 400°C, and most preferably less than 350°C. Preferably, the elevated temperature is between 50°C and 550°C, more preferably between ioo°C and 500°C, between 150°C and 450°C, or between 200°C and 400°C, and most preferably between 250°C and 350°C.

Preferably, the method comprises increasing the temperature of the feedstock to the elevated temperature. Preferably, the method of increasing the temperature of the feedstock comprises positioning a solar thermal collector to focus light on or adjacent to the feedstock.

Preferably, the method comprises increasing the pressure of the feedstock to the elevated pressure. Preferably, the method of increasing the pressure of the feedstock comprises increasing the temperature of the feedstock. Advantageously, as the temperature increases, sub-super-critical water is formed and the pressure increases.

Preferably, the elevated pressure is at least 5 MPa, more preferably at least 7.5 MPa, at least 10 MPa or at least 12.5 MPa, most preferably at least 15 MPa. Preferably, the elevated pressure is less than 50 MPa, more preferably less than 40 MPa, less than 30 MPa or less than 25 MPa, and most preferably less than 20 MPa. Preferably, the elevated temperature is between 5 MPa and 50 MPa, more preferably between 7.5 MPa and 40 MPa, between 10 MPa and 30 MPa, or between 12.5 MPa and 25 MPa, and most preferably between 15 MPa and 20 MPa.

Preferably, if the pressure rises above the elevated pressure then the method comprises reducing the pressure to the elevated pressure. Preferably, reducing the pressure comprises venting feedstock from the at least one processing conduit.

Preferably, the steps of increasing the temperature of the feedstock and increasing the pressure of the feedstock are conducted subsequent to the step of feeding the feedstock into the at least one processing conduit. Preferably, the method comprises maintaining the feedstock at the elevated

temperature and pressure for at least 1 minute, more preferably at least 5 minutes or at least 10 minutes, and most preferably at least 15 minutes. Preferably, the method comprises maintaining the feedstock at the elevated temperature and pressure for less than 120 minutes, more preferably less than 60 minutes or less than 45 minutes, and most preferably less than 30 minutes. Preferably, the method comprises maintaining the feedstock at the elevated temperature and pressure for between 1 minute and 120 minutes, more preferably between 5 minutes and 60 minutes or between 10 minutes and 45 minutes, and most preferably between 15 minutes and 30 minutes.

Preferably, the step of feeding the coolant into the heat exchange conduit comprises reducing the temperature of the product to less than 250°C, more preferably less than 200°C, less than i8o°C, less than i6o°C, less than 140°C or less than 120°C, most preferably less than ioo°C, less than 90°C or less than 8o°C. Preferably, the step of feeding the coolant into the heat exchange conduit comprises reducing the temperature of the product to between 30°C and 250°C, more preferably between 35°C and 200°C, between 40°C and i8o°C, between 45°C and i6o°C, between 50°C and 140°C or between 55°C and 120°C, most preferably between 6o°C and ioo°C, between 65°C and 90°C or between 70°C and 8o°C.

Preferably, prior or simultaneously to feeding the coolant into the heat exchange conduit, the method comprises positioning the solar thermal collector to reduce the light focused on or adjacent to the feedstock.

Preferably, subsequent to feeding the coolant into the heat exchange conduit, the method comprises venting the heat exchange conduit. Venting the heat exchange conduit may comprise slushing the heat exchange conduit with air. Advantageously, in subsequent heating cycles, energy will not be wasted heating the coolant.

The method may comprise collecting the product. The method may comprise purifying the bio-oil. The bio-oil may be purified by solid separation primary filtration of solid char fractions followed by gravitation or centrifugation separation of aqueous, solid and oil phases. The method may comprise bio-oil upgrading by catalytic hydrogenation prior to petroleum refining.

The method may comprise preheating the feedstock. Preferably, the method comprises preheating the feedstock prior to feeding the feedstock into the at least one processing conduit. Preferably, preheating the feedstock comprises:

feeding the feedstock into a feedstock inlet conduit, wherein the feedstock inlet conduit is configured to feed the feedstock into the at least one processing conduit; and

feeding the coolant into a coolant outlet, wherein the coolant outlet is configured to receive coolant from the heat exchange conduit and is disposed at least substantially adjacent to the feedstock inlet conduit, to increase the temperature of the feedstock disposed in the feedstock inlet conduit.

Advantageously, the preheating step utilises the heat recovered from a previous reaction cycle to pre-heat the feedstock. This reduces the time taken to heat the feedstock. All features described herein (including any accompanying claims, abstract and drawings), and/ or all of the steps of any method or process so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and/ or steps are mutually exclusive. Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a side view of a hydrothermal liquefaction (HTL) reactor;

Figure 2 is a cross-sectional view of an inlet region of a HTL rector;

Figure 3 is a cross-sectional view of a processing region of a HTL rector taken along line II shown in Figure 1;

Figure 4 is a cross-sectional view of a processing region of a HTL rector taken along line III shown in Figure 1;

Figure 5 is a perspective view the processing region of the HTL reactor;

Figure 6 schematically shows reactor core pipes of the HTL reactor; and

Figure 7 is a perspective view the HTL reactor positioned in the focal point of a concentrated solar power (CSP) parabolic trough.

A solar receiver hydrothermal liquefaction (HTL) reactor 2 is shown in Figure 1. It will be appreciated that the size of a HTL reactor 2, and its constituent parts, will vary depending on the CSP focal point and aperture of solar collectors it is intended to be used with. Accordingly, the sizes given below are by way of example only.

The HTL reactor 2 will comprise a feedstock intake region 4, a processing region 6 and a product outlet region 8. Figures 2 and 3 show cross-section views of the feedstock inlet region 4 and Figure 4 shows a cross-section view of the processing region 6. While not shown, it will be appreciated that the cross-section of the product outlet region 8 will substantially correspond to the cross-section of the inlet region 4. As shown in Figure 3, in a section of the feedstock intake region 4 spaced apart from the processing region 6, the HTL reactor comprises an inner pipe 12 with an outer diameter of 180 mm. The inner pipe 12 comprises a 1 mm thick metal or metal alloy comprising aluminium, copper, steel and/or titanium. The inner pipe 12 encloses an outer feedstock pipe 20 and the space 26 between the outer feedstock pipe 20 and the inner pipe 12. The space between the inner pipe 12 and the outer feedstock pipe 20 is minimal and may comprise a mineral oil.

The outer feedstock pipe 20 comprises a pressure resistant stainless steel tube with a thickness between 1 mm and 10 mm. The internal surface of the outer feedstock pipe 20 may be coated with an anti-corrosion substance, such as a thermally sprayed ceramic layer comprising approximately 60% Al ₂ 0 ₃ and 40% Ti0 ₂ . The outer feedstock pipe 20 is a pressure vessel i.e. it is configured to withstand pressures of at least 25 MPa and 400°C. The outer feedstock pipe 20 defines a feedstock conduit 22 configured to receive a HTL feedstock, e.g. biomass suspended in water. A first pressure relief valve (not shown) is disposed in this section of the feedstock conduit to control the flow of feedstock along the conduit as explained below. A corresponding second pressure relief valve (not shown) is disposed in the corresponding section of the product outlet region 8. As shown in Figure 1, closer to the processing region 6, a heat exchange pipe 16

penetrates through the walls of the inner pipe 12 and the outer feedstock pipe 20 and then diverts at an angle to extend through the processing region 6 and into the product outlet region 8, where the heat exchange pipe 16 then diverts at an angle again to penetrates through the walls of the inner pipe 12 and an outer product pipe 32. The heat exchange pipe 16 is made of a 1 mm thick metal or metal alloy comprising aluminium, copper, steel and/or titanium. The heat exchange conduit has an outer diameter of 50 mm. The heat exchange pipe is configured to hold a coolant, such as liquid nitrogen, which acts to quickly reduce the temperature of the core of the reactor following the HTL reaction. A valve (not shown) is disposed in the heat exchange conduit in the product outlet region to control the flow of coolant in the conduit.

Accordingly, as shown in Figure 2, in the feedstock inlet region 4 adjacent to the processing region 6 the HTL reactor 2 comprises an inner feedstock pipe 18, disposed adjacent to and surrounding the heat exchange pipe 16 and having an external diameter of 54 mm. The inner feedstock pipe comprises the same material as the outerfeedstock pipe. The outer feedstock pipe 20 is disposed adjacent to and surrounded by the inner pipe 12.

The space 24 between the heat exchange pipe 16 the inner feedstock pipe 18, and the space 26 between the outer feedstock pipe 20 and the inner pipe 12 are minimal. Any space may comprise a mineral oil. This will be beneficial as it will aid insertion of the pipes during manufacture and will also improving heat flow characteristics of the final reactor 2.

At the point where the intake region 4 changes to the processing region 6, the inner and outer feedstock pipes 18, 20 are configured to split into a plurality of processing pipes 28 with an external diameter of 15 mm, as shown schematically in Figure 6. The thickness of the stainless steel in the processing pipes 28 will be between 0.5 mm and 3.5 mm. It will be appreciated that the processing pipes 28 are also pressure vessels and are configured to receive a HTL feedstock and comprise pressure resistant stainless steel tube which may be coated internally with an anti-corrosion substance. Similarly, at the point where the processing region 6 changes to the outlet region 8, the plurality of processing pipes 28 converge to define an inner product pipe (not shown) and an outer product pipe 32.

As shown in Figures 1 and 4, in the processing region 6 the HTL reactor comprises an outer pipe 10 with an outer diameter of 200 mm. It will be noted that in the embodiment illustrated, the feedstock intake region 4 and product outlet region 8 do not comprise the outer pipe 10. The outer pipe 10 comprises an insulated glass with a thickness of 10 mm and encloses an inner pipe 12 with an outer diameter of 180 mm. In the processing region 6, the external surface of inner pipe is painted matt black to enhance its heat conductivity properties. The space 14 between the outer pipe 10 and the inner pipe 12 is about 10 mm wide and comprises a vacuum. It will be appreciated that a vacuum increases the cost of the apparatus, so in some embodiments the space 14 may instead comprise a gas, such as air. The vacuum (or airspace) acts as an insulator to prevent thermal losses due to external air circulation.

Accordingly, as shown in Figures 4 and 5, in the processing region 6, a plurality of processing pipes 28 are disposed in the space between the inner pipe 12 and the heat exchange pipe 16. In the illustrated embodiment about a hundred processing pipes 28 are disposed in four layers in the space 30. However, it will be appreciated that the exact number of processing pipes 28 provided may vary. Air or an inert mineral oil is disposed between the processing pipes 28. The processing pipes 28 may be orientated so that their outer surface touch the outer surface of one or more other processing pipes 28, the internal surface of the inner pipe 10, and/ or the outside surface of the heat exchange pipe 16.

In the illustrated embodiment, the heat exchange pipe 16 is disposed in the centre of the HTL reactor 2. However, in an alternative embodiment, the heat exchange pipe may be disposed between the outer pipe 10 and inner pipe 12. In this embodiment, the processing pipes 28 would be disposed in the centre of the HTL reactor 2.

As shown in Figure 7, the reactor 2 may be disposed along the focal line 34 of a parabolic trough 36. The parabolic trough 36 comprises curved mirrors 38 which focus the energy from sunlight along the focal line.

During operation, the pressure relief valve disposed in the intake region 4 is opened, and a feedstock is fed through the feedstock conduit 22 and into the processing pipes 28. The pressure relief valve disposed in the outlet region 8 holds the feedstock in the processing region 6. The feedstock comprises approximately 20% (w/v) microalgae suspended in water. The feedstock may also comprise a catalyst, such as about 0.1% (w/v) Na ₂ C0 ₃ . Due to the reactor 2 being disposed within the parabolic trough 36, the temperature of the feedstock will then be raised to 350°C. Depending upon the intensity of the sun, etc., this step will take about 20 minutes. As the temperature of the feedstock increases, sub-super-critical water is formed and this also causes the pressure to increase. The pressure relief valves are configured to vent feedstock from the processing pipes 28 if the pressure rises above 20 MPa. The feedstock will then be held at the increased temperature and pressure for 20 minutes. This will cause the feedstock to undergo hydrothermal liquefaction (HTL), and will thereby convert the feedstock to a product, comprising 70-80% (w/v) water, 20-25% (w/v) bio-oil, 1-5% ( /v) solids including bio-char and <2% (w/v) gases.

Once the reaction is complete the bio-oil, bio-char and organic gas fractions contained within the processing pipes 28 are cooled. This is achieved by rotating the mirrors 38 away from direct sunlight.

The temperature of the processing conduits is allowed to drop to a predetermined temperature, which is monitored using a thermocouple (not shown) disposed in the processing region 6. Once the predetermined temperature has been reached the valve in the heat exchange pipe 16 is opened and coolant is fed through the heat exchange pipe 16 to further cool the processing conduits. This step will take about 20 minutes.

In a preferred embodiment, the coolant is fed from a heat exchange inlet conduit, disposed in product outlet region 8, through the heat exchange pipe 16 and then through a heat exchange outlet conduit, disposed in feedstock inlet region 4.

Advantageously, the coolant transfers heat to feedstock disposed in the feedstock inlet region 4, thereby preheating feedstock which may be used in the next reaction cycle.

Once the bio-oil, bio-char and organic gas fractions have been cooled to 8o°C, they are fed through the outlet region 8 and collected for further processing into water solubles, bio-oil and char solid fractions.

It will be appreciated that this method could be controlled manually. However, in a preferred embodiment, the apparatus comprises control means configured to automatically control the reaction process.