BOTTOMING CYCLE

Field of the Invention

This invention relates to combustion systems for industrial processes, including but not limited to electric power generation. More particularly, the invention relates to a high pressure oxy-fuel system, and the delivery of thermal energy from condensation from the flue gas of the high pressure oxy-fuel system to an organic Rankine cycle system.

Concurrently, direct thermal energy from the combustion in the system of the invention can be provided to a Rankine cycle or a wide variety of other systems.

Background of the Invention

In the ongoing aim to reduce the emission of greenhouse gases in industrial processes which generate carbon dioxide, but while continuing to use fossil fuels which are generally otherwise preferable over other fuels for practical and economic reasons, attempts have been made to simplify the isolation of the carbon dioxide so that it can be removed from the processes for sequestration or other containment or use. In particular, it has been found that the replacement of ambient air by concentrated oxygen in what are known as oxy-fuelled or oxy- fired combustion processes is advantageous in that the absence of the high levels of nitrogen and other constituents in air, thus avoiding the need to separate either the nitrogen or other constituents. Further, the absence of nitrogen avoids the formation of NOx and other problematic compounds, and the high costs in situations where these are required to be separated. Oxy-fuel systems thus result in a flue gas which has a high purity level of carbon dioxide and requires minimal or no further separation treatment before being prepared, for example by pressurization, for sequestration or use.

Oxy-fuel systems are advantageous in that they provide relatively simple solutions which are applicable to new systems or the retrofit of existing systems. However, such systems when operated at ambient pressure suffer from disadvantages of inefficiency, as well as the higher costs arising from the need for an air separation unit for provision of the oxygen, and the costs of the carbon dioxide product recovery train.

Oxy-fuel systems operate at significantly higher temperatures than air- fired systems, and thus require temperature control. There are various known methods of temperature moderation, including staging, the use of fluid beds, or the recirculation of a portion of the flue gas back to the combustor.

It has therefore been proposed to use high pressure for oxy-fuel systems, to address at least some of the above disadvantages, and to allow for a significant reduction in size for the structures used. For example, US 6,196,000 (Fassbender) proposes a pressurized Rankine cycle oxy-fuel system, allowing for reduced equipment size, and for condensing the carbon dioxide at ambient heat-sink temperatures, thus minimizing the need for multistage compression and refrigeration; and for increased efficiency from the use of waste heat to replace regenerative extraction from the turbine. However, the proposed system suffers from various disadvantages, some of which apply to oxy-fuel systems in general, including increased costs for high pressure oxygen feed, and difficulty in achieving temperature moderation using flue gas as recirculation. The proposed system included the variation in the conventional configurations of feedwater heaters, by removing some of them and instead using heat from condensed moisture in the flue gas. However, conventional feedwater heater arrangements are highly developed and efficient, and any changes in those result in the need to adjust various other aspects of the system, including to address the effects of altering the regenerative extraction from the turbine; problems in making such adjustments present a significant disadvantage of the proposed system.

One advantage of high pressure operation is that it changes the temperature condition at which the gas to liquid phase change occurs for the flue gas, which thus allows for water vapour in the flue gas to be condensed at much higher temperatures than in air-fired systems. For example, moisture in the flue gas condenses in the range of 150°C to 200°C at 80 bar, as compared with 50°C to 55°C in ambient pressure oxy-fuel systems. It has now been found that this, and other advantages, makes the condensate from the flue gas of a pressurized oxy-fuel system a suitable heat source for use in various processes, including but not limited to power generation systems and similar systems, including Brayton cycles, Rankine cycles and binary fluid cycles, and it is particularly

advantageous to use such flue gas condensate to provide heat to organic Rankine cycles. It has further been found advantageous to use the direct heat of the combustor of the system and the method of the invention to provide a direct heat energy source for various secondary systems, including but not limited to Brayton cycles, Rankine cycles and binary fluid cycles. Further, it has been found to be particularly advantageous to provide the heat of the condensate as a bottoming cycle to an organic Rankine cycle system, and to provide the direct heat of the combustion within a secondary Rankine cycle system, without making any modification to the conventional feedwater heater arrangements.

Summary of the Invention

The invention therefore seeks to provide a combustion system for operational connection to an industrial process system, the combustion system comprising

(a) a combustor constructed and arranged to be selectively operable at a selected operational pressure exceeding atmospheric pressure, and comprising

(i) a combustor wall comprising a combustion chamber;

(ii) a burner;

(iii) at least a first fuel inlet constructed and arranged to deliver a first fuel to the burner at a delivery pressure exceeding the selected operational pressure;

(iv) at least one oxidant inlet constructed and arranged to deliver a supply of oxygen having a purity of at least 22% to the burner at a delivery pressure exceeding the selected operational pressure;

(v) an outlet region having a flue gas outlet;

(b) a flue gas delivery means, constructed and arranged to be operatively connected to the flue gas outlet, to receive a supply of flue gas therefrom at a pressure exceeding atmospheric pressure and to deliver at least part of the supply of flue gas to a heat removal means comprising

(i) at least one condensing means to produce condensate from the supply of flue gas; and

(ii) a heat delivery means to deliver heat from the condensate to the industrial process system.

Preferably, the condensing means and the heat delivery means comprise at least one condensing heat exchanger.

Preferably, the first fuel inlet is constructed and arranged to deliver a first fuel selected from at least one of a solid fuel, a liquid fuel, a gaseous fuel, and combinations thereof.

Preferably, the at least one oxidant inlet is constructed and arranged to deliver a supply of oxygen having a purity of at least 80%, more preferably at least 95%.

Optionally, the flue gas delivery means comprises a flue gas recirculation outlet and the combustor further comprises at least one flue gas recirculation inlet, and the flue gas recirculation outlet is constructed and arranged to selectively deliver a supply of part of the flue gas to selective ones of the at least one flue gas recirculation inlet.

The industrial process system can be a power generation system, for example an electric power generation system. Alternatively, the combustion system is constructed and arranged to be operationally connected to and deliver the heat from the condensate to a low temperature power cycle system.

In some embodiments, the combustion system is constructed and arranged to be operationally connected to and deliver the heat from the condensate to a system selected from a Brayton cycle system, a Rankine cycle system, and a binary fluid cycle system. Preferably, the combustion system is constructed and arranged to be operationally connected to and deliver the heat from the condensate to an organic Rankine cycle system.

Where the combustion system is constructed and arranged to be operationally connected to a binary fluid cycle system, preferably that system is a Kalina cycle.

Preferably, the combustor is further constructed and arranged to be operationally connected to and deliver direct heat to a secondary system. Such secondary system can be selected from an engine, a secondary industrial process system and a secondary power system; and selected from a Brayton cycle system, a Rankine cycle system, and a binary fluid cycle system. Where the secondary system comprises a binary fluid cycle system, preferably it is a Kalina cycle.

In some embodiments, the secondary system is a secondary industrial process system comprising a Rankine cycle system having a flow path for a flow of working fluid, the flow path being constructed and arranged to deliver the flow through a low pressure turbine, and thereafter to deliver at least part of the flow selectively to an evaporator in the organic Rankine cycle system. The invention therefore further seeks to provide a method of providing heat energy to an industrial process system, the method comprising the steps of

(a) providing a combustion system according to the invention and selecting an operational pressure;

(b) connecting the flue gas delivery means to the heat removal means, and connecting the heat removal means to the industrial process system;

(c) delivering a supply of the first fuel to at least the first fuel inlet at a delivery pressure exceeding the selected operational pressure;

(d) delivering a supply of oxygen having a purity of at least 22% to the burner at a delivery pressure exceeding the selected operational pressure; (e) operating the combustor at the selected operational pressure to generate a supply of flue gas, and delivering at least part of the supply of flue gas to the heat removal means;

(f) producing condensate from the supply of flue gas, and delivering heat from the condensate to the industrial process system.

Preferably, step (d) comprises delivering a supply of oxygen having a purity of at least 80%, more preferably at least 95%.

Optionally, step (b) comprises providing the flue gas delivery means with a flue gas recirculation outlet and step (e) further comprises delivering at least a part of the supply of flue gas through the recirculation outlet and into the combustor.

The invention therefore further seeks to provide a method of providing heat energy to an industrial process system, the method comprising the steps of

(a) providing a combustion system according to the invention and selecting an operational pressure;

(b) connecting the flue gas delivery means to the heat removal means, and connecting the heat removal means to the industrial process system;

(c) connecting the combustor to the secondary system;

(d) delivering a supply of the first fuel to at least the first fuel inlet at a delivery pressure exceeding the selected operational pressure;

(e) delivering a supply of oxygen having a purity of at least 22% to the burner at a delivery pressure exceeding the selected operational pressure;

(f) operating the combustor at the selected operational pressure to produce heat energy and generate a supply of flue gas;

(g) delivering heat energy to the secondary system and delivering at least part of the supply of flue gas to the heat removal means;

(h) producing condensate from the supply of flue gas, and delivering heat from the condensate to the industrial process system. Preferably, step (e) comprises delivering a supply of oxygen having a purity of at least 80%, more preferably at least 95%.

Optionally, step (b) comprises providing the flue gas delivery means with a flue gas recirculation outlet and step (g) further comprises delivering at least a part of the supply of flue gas through the recirculation outlet and into the combustor.

Brief Description of the Drawings

The invention will now be described with reference to the drawings, in which

Figure 1 is a schematic representation of a conventional layout of a Rankine cycle system of the prior art;

Figure 2 is a schematic representation of a combustion system in an embodiment of the invention;

Figure 3 is a schematic representation of a combustion system in a second embodiment of the invention; and

Figure 4 is a schematic representation of a combustion system in a third embodiment of the invention.

Detailed Description of the Drawings

Referring to Figure 1 , this is a schematic representation of a conventional layout of a Rankine cycle system 10 of the prior art. Various layouts are known and used, but in accordance with the principles of operation of such cycles, each includes at least the elements shown in Figure 1. In sequence, the working fluid (not shown) passes through boiler/evaporator 1 1, is expanded in turbine 13, passes through regenerator (also known as recuperator) 14, and thence to condenser 15. From condenser 15, the working fluid is pumped by pump P, and passed through regenerator 14 for preheating before being returned to boiler/evaporator 11.

Referring now to Figure 2, an embodiment of the invention is shown in a schematic representation, in which furnace 30 is operationally connected to an organic Rankine cycle 220, and a secondary Rankine cycle 50. Organic Rankine cycle 220 comprises high temperature evaporator 21, turbine 23, regenerator 24 and condenser 25, and will have a suitable working fluid selected from those known and permitted to be used pursuant to any applicable regulations.

Furnace 30 is designed for high pressure oxy-firing, and is fed by fuel supply from line 32 at fuel inlet 33, and oxygen supply from line 34 at oxygen inlet 35. Oxygen is supplied at the selected level of purity, by known methods, for example from an air separation unit (not shown). Flue gas generated by the combustion leaves furnace 30 in flue gas line 36. Optionally, a recirculation stream can be separated from the flue gas stream in flue gas line 36, to be selectively recirculated back in flue gas recirculation line 38 to be reintroduced to the furnace in a suitable manner, either through a separate inlet (not shown) or by joining the oxygen supply in line 34. The main flue gas stream is delivered to a condenser 40 at flue gas inlet 39. Condenser 40 can be of any known construction, and is preferably a condensing heat exchanger.

In condenser 40, water is condensed from the flue gas stream, the condensate passes through condensate line 42 to be delivered to high temperature evaporator 21 at condensate inlet 43, and the heat of condensation is provided to high temperature evaporator 21 , to contribute to the heating of the working fluid in organic Rankine cycle 220. The remaining gaseous portion of the flue gas stream, mostly pressurized carbon dioxide, leaves condenser 40 at outlet 44, and passes through line 45 to a carbon dioxide capture system 46, where impurities are removed by known means, and the carbon dioxide product stream is removed for further processing, use or sequestration .

Concurrently with providing heat of condensation to organic Rankine cycle 220, furnace 30 can be used to provide direct heat of combustion to various types of system requiring heat energy. In the exemplary embodiment of Figure 2, furnace 30 is shown as operationally connected to a Rankine cycle 50 of a conventional configuration and shown here as having water as the working fluid. In Rankine cycle 50, expanded working fluid leaves intermediate pressure/low pressure turbine 52, passes through and is condensed in condenser 56, and passes to a first group of feedwater heaters 53, shown here as feedwater heaters 53a, 53b and 53c. Extracted heat can be selectively provided to each of feedwater heaters 53a, 53b and 53c from intermediate pressure/low pressure turbine 52. The working fluid then passes to a second group of feedwater heaters 55, shown here as feedwater heaters 55a and 55b. Extracted heat can be selectively provided to each of feedwater heaters 55a and 55b from high pressure turbine 54. The working fluid then passes to reheater 57, which is supplied with heat from furnace 30, and delivered to and expanded in high pressure turbine 54 to provide energy to the process or system being powered by Rankine cycle 50. Thereafter, the working fluid is reheated in reheater 58, which is also supplied with heat from furnace 30, before passing to and being expanded in intermediate pressure/low pressure turbine 52 to provide energy to the process or system being powered by Rankine cycle 50, and to complete the cycle. In each of Figures 2 to 4, it will be appreciated that various known structural elements will be included in the embodiments of the invention, such as pumps, valves etc. For simplification, these are not included in the figures in general, but some of the pumps are included where this would assist in understanding the invention, and are identified generically as P.

Referring now to Figure 3, a second exemplary embodiment of the invention is shown in a schematic representation. In this embodiment, again furnace 30 supplies the heat of condensation of flue gas to organic Rankine cycle 320, in the same manner as in the configuration shown in Figure 2; and provides direct heat to Rankine cycle 350, which is shown as having water as the working fluid. However, organic Rankine cycle 320 is provided with a low temperature evaporator 22, which preheats the working fluid of organic Rankine cycle 320 after the working fluid leaves regenerator 24 and before it enters high temperature evaporator 21. Working fluid from Rankine cycle 350 leaving intermediate pressure/low pressure turbine 52, instead of passing directly to steam condenser 56, passes in line 70 to low temperature evaporator 22, where it provides heat to the working fluid of organic Rankine cycle 320. Thereafter the working fluid in Rankine cycle 350 returns in line 72 to steam condenser 56.

Referring now to Figure 4, a further exemplary embodiment of the invention is shown in a schematic representation. In this embodiment, again furnace 30 supplies the heat of condensation of flue gas to organic Rankine cycle 420, in the same manner as in the configurations shown in Figures 2 and 3; and provides direct heat to Rankine cycle 450, which is shown as having water as the working fluid. Further, in the same manner as in the configuration shown in Figure 3, organic Rankine cycle 420 is provided with low temperature evaporator 22, which preheats the working fluid of organic Rankine cycle 420 after the working fluid leaves regenerator 24 and before it enters high temperature evaporator 21. However, in this embodiment, when the working fluid from Rankine cycle 450 leaves intermediate pressure/low pressure turbine 52, it is split into two streams, one of which passes in line 470 to low temperature evaporator 22, where it provides heat to the working fluid of organic Rankine cycle 420, before returning in line 472 to the input region 60 of steam condenser 56, where it is joined by the second stream passing directly to steam condenser 56 from intermediate pressure/low pressure turbine 52 in line 474.

As noted above, the system and methods of the invention provide an advantageous use for condensate in the flue gas of a pressurized oxy-fuel system, which can be readily connected to many types of conventional systems, without requiring significant modification to those systems, which is of particular significance in relation to (1) delivery of the thermal energy from condensation to all manner of organic Rankine cycles; and (2) connection to Rankine cycles for the provision of direct heat from the combustor, where the connection of the system of the invention to the Rankine cycle can be made without requiring any modification to the highly developed and complex arrangements for the feed water heaters.