NL2021512B1 - System for generating energy in a working fluid from hydrogen and oxygen and method of operating this system - Google Patents

Abstract

A system for generating energy in a working fluid from hydrogen and oxygen, comprises a burner (12) for combustion of hydrogen and oxygen into steam provided with a feed (14) for 5 oxygen and a feed (16) for hydrogen, a boiler (22) operably connected to the burner for heating the working fluid having a feed (24) for introducing the working fluid and a discharge (26) for discharging heated working fluid and a heat exchanging surface (25) for heat exchange between the steam and the working fluid, a condenser (30) for condensing steam operably connected to the boiler downstream thereof, 10 wherein a recirculation loop (32; 55; 57) is provided for recirculation of reaction products of the combustion of hydrogen and oxygen downstream of the condenser to the burner, and a recovery loop (38) for recycling oxygen separated in the separator from the separator to the feed of oxygen of the burner. 15 Fig. 3

Description

SYSTEM FOR GENERATING ENERGY IN A WORKING FLUID FROM HYDROGEN AND OXYGEN AND METHOD OF OPERATING THIS SYSTEM

The present invention relates to a system for generating energy in a working fluid from hydrogen and oxygen, as well as to an operating method thereof.

Hot water boilers, steam boilers and furnaces are well known apparatuses for producing heated water, steam and/or other working fluids. These prior art boilers and furnaces are operated by fossil fuels, like coal, oil and natural gas. The produced hot water, steam and/or other working fluids can be used as such, e.g. for heating purposes in industrial processes, or fed to turbines and/or generators for generating electricity in power plants. Fossil fuels produce flue gasses including carbon dioxide and NOx which compounds are considered harmful to the environment. Because thereof the use of alternative, renewable energy sources like solar, wind and wave has gained much interest. The uncertainty of the continuous availability of these energy sources is however a serious disadvantage for application in continuous processes. Temporary storage of the energy generated, e.g. as hydrogen, is envisaged and implemented.

A water fuelled boiler using electrolysis to convert water to high pressure steam is known from US5279260A. In such a system water is dissociated in an electrolysis tank provided with electrodes into oxygen and hydrogen. These products are ignited to produce high pressure steam that can be used e.g. for heating purposes or operating a steam engine or turbine. US5177952A has disclosed a power system adaptable for use in terrestrial and extraterrestrial applications, which system comprises a catalytic combustor for combusting a fuel (hydrogen) and an oxidizer (oxygen) at stoichiometric conditions. The combustion efflux is combined with a third product to form a working fluid, typically steam. The working fluid is used to drive an engine, a controlled portion of the exhaust of which is cooled and condensed in a condenser and fed to an electrolysis unit for reconstitution of the fuel and oxidizer, that can be temporarily stored for ultimate reuse in the combustor.

Power systems based on the reaction between oxygen and hydrogen do not emit harmful exhaust gasses to the environment. However, although the system of US5177952A is said to be a closed cycle power system, nevertheless the fuel cycle and the working fluid cycle in this known system are interconnected, which may result in undesirable leakage of steam and thus starting material from the system as well as leakage of environmental air into the system. Both types of leakage will affect the operation of the system. In particular, contamination of the starting water is detrimental.

-2It is also known that the combustion temperature of pure oxygen and hydrogen is very high, such that the systems in particular the burner, fire box and other boiler parts have to be made from specific materials with extreme heat-resistance properties.

An object of the present invention is to provide a system for generating energy in a working fluid from hydrogen and oxygen, which does not show the disadvantages of the above prior art systems or at least to a lesser extent.

Another object of the invention is to allow manufacturing the system, in particular the burner or combustor, from conventional materials.

According to the invention a system for generating energy, in particular heat, in a working fluid from hydrogen and oxygen comprises:

a burner for combustion of hydrogen and oxygen into steam provided with a feed for oxygen and a feed for hydrogen, a boiler operably connected to the burner for heating the working fluid having a feed for introducing the working fluid and a discharge for discharging heated working fluid and a heat exchanging surface for heat exchange between the steam and the working fluid, a condenser for condensing steam operably connected to the boiler downstream thereof, wherein at least one recirculation loop is provided downstream of the boiler for recirculation of reaction products of the combustion of hydrogen and oxygen to the burner, and a recovery loop for recycling excess oxygen separated in the condenser to the feed of oxygen of the burner.

The system according to the invention comprises a burner or combustor that is typically provided with an interrupted ignition element, wherein oxygen and hydrogen as raw materials are allowed to react to form steam. The burner is operably connected to a boiler wherein the steam that has been produced in the burner is subjected to a heat exchange (typically heat pipes through which the working fluid is forced to flow) with a working fluid thereby increasing the heat content of the working fluid, such as hot water or steam. Other examples of working fluid include (thermal) oils, fluid flows of (intermediate) compounds in chemical processes,

e.g. petrochemical processes. It should be understood that in the context of this application the term “boiler” encompasses both boilers, wherein the working fluid is water that is heated to hot water or steam, as well as furnaces, wherein the working fluid is a medium other than water or steam, like the examples presented above. Throughout this application the single term “boiler” is used to indicate a boiler or a furnace, unless from the context it is apparent that boiler is used in a limited sense. The working fluid heated in the boiler can be used, e.g. for heating purposes in an industrial plant as well as generation of energy. Advantageously the burner and boiler form a single integrated unit. The heat exchanged steam is passed from the boiler to a condenser, where the steam condenses into water. The water may be used as such for various purposes.

-3According to the invention the oxygen/hydrogen/steam and water circuit and the working fluid circuit are not interconnected, but are separated entirely using the heat exchanging surface in the boiler, which results in a robust and versatile system. In order to reduce the combustion temperature in the burner a partial flow of reaction products resulting from the combustion of hydrogen and oxygen that have been subjected to heat exchange with the working fluid, is recycled back to the burner thereby controlling the temperature thereof and the reaction between oxygen and hydrogen. This temperature reduction by recycling steam also allows to use conventional boiler designs and materials. The reaction products downstream of the boiler comprise water, whether in the form of steam or liquid as will become apparent hereinafter. Additionally excess oxygen is separated in the condenser and fed into the recovery loop of oxygen. The separated oxygen is returned to the oxygen feed of the burner, in particular to the inlet of the burner. Excess oxygen is necessary for the complete combustion of hydrogen in the burner.

In an embodiment the recirculation loop for recirculation of reaction products is configured downstream of the boiler and upstream of the condenser for recirculation of non-condensed steam to the burner.

In another embodiment the recirculation loop is configured for recirculation of condensate from the condenser to the burner.

In yet another embodiment the system further comprises a separator for separating oxygen from the condensate (i.e. condensed steam) operably connected to the condenser. In the additional oxygen separator oxygen is separated downstream of the condenser from the water derived from the steam. A deaerator is a typical example of a suitable separator. Although the main portion of the oxygen excess is separated from the steam in the condenser, the condensate (water) may comprise still some oxygen. In the oxygen separator full recovery of oxygen can be accomplished. Preferably the separator is provided with a discharge of separated oxygen that is operably connected to the recovery loop for recycling oxygen. By incorporation of the condenser and optionally the oxygen separator in the circuit the system can be operated under a slight stoichiometric excess of oxygen ensuring a complete combustion of hydrogen.

The water from which oxygen is removed in the separator can also be used to control the combustion reaction in the burner by configuring the recirculation loop downstream of the separator for recirculation of the condensate after treatment in the separator to the burner. In the various embodiments recirculation of steam downstream of the boiler, recirculation of condensate downstream of the condenser and upstream of the separator, and/or deoxygenated water downstream of the separator serve the purpose of controlling the combustion reaction of oxygen and hydrogen in the burner. Thus the recirculation loop may

-4be configured as a single loop based on any one of the above embodiments, but may also comprise any combination of the above embodiments.

Existing boilers can be easily retrofitted to the system according to the invention by altering its feed to the burner and addition of a recycling loop, such as a steam recovery loop, and oxygen recovery loop as described above.

In a further embodiment the system according to the invention also comprises an electrolyser for electrolysis of water into oxygen and hydrogen having a feed for water operably connected to the separator, and outlets for oxygen and hydrogen respectively, operably connected to the respective feed of the burner. In this way the deoxygenated water from the separator is reused for reconstitution of the starting materials oxygen and hydrogen for reaction in the burner and the system can be operated without a constant supply of fresh hydrogen and fresh oxygen, except for some make-up water due to inevitable losses from leakage.

Preferably the system according to the invention also comprises a storage of oxygen and a storage of hydrogen operably connected to the outlets of the electrolyser and upstream of the burner. By incorporation of buffers of oxygen and hydrogen respectively between the electrolyser and the burner a continuous operation of the system can be ensured. The oxygen and hydrogen may be stored in any suitable form, e.g. as pure compounds. In an embodiment hydrogen is converted into a chemically bounded compound, like metal hydrides that can be easily stored. Buffering is particularly advantageous if the electrolyser is powered from non-fossil sources, like wind, solar and wave, the electricity generation of which is dependent on its availability due to the day/night rhythm and weather conditions.

Hereinafter the invention is illustrated by means of the attached drawing, wherein: Fig. 1 shows an embodiment of the system according to the invention;

Fig. 2 shows a further embodiment of the system according to the invention; and Fig. 3 shows an embodiment of an extended system according to the invention. In Fig. 1 an embodiment of the system for generating energy in a working fluid of the invention is shown diagrammatically. The system, indicated in its entirety by reference numeral 10, comprises a burner or combustor 12 for conversion of oxygen and hydrogen into steam. Oxygen and hydrogen are supplied as pure starting materials via supply lines 14 and 16 respectively from suitable sources. In the burner 12 upon ignition the oxygen and hydrogen are converted into steam having a high temperature. In the boiler 22 the steam as produced transfers a part of its heat to a working fluid, typically water thereby generating heated water and/or steam to be used in another process. The working fluid is supplied by supply line 24 to heat pipes 25 arranged in the boiler 22 and the energized working fluid is discharged from the boiler 22 via discharge conduit 26. The working fluid can be used as such e.g. in industrial processes, as a heating medium or for driving a turbine in order to generate electricity. The primary steam after heat exchange exits the boiler 22 through outlet to condenser 30, where the primary steam is condensed. In order to reduce the operating temperature of the combustor 12 a partial flow of primary steam controlled by control valve 31 is recycled to the burner 12 for cooling thereof via recycle conduit 32 and pump or fan 34. The main flow of primary steam is condensed to water in the condenser 30, where remaining oxygen, is removed from the water. The water leaves the condenser 30 through discharge conduit 35. The oxygen separated in condenser 30 is returned to the oxygen feed, in particular the inlet 37 of burner 12 via return conduit 38 and fan 39.

In this Fig. also a recirculation conduit 55 and associated pump 56 for recirculation of a partial flow of condensate from the condenser 30 to the burner 12 is shown. This conduit 55 fluidly connects the condenser 30 to the burner 12.

As shown in the embodiment of Fig. 2, wherein the same parts bear the same reference numerals, the water obtained in condenser 30 is further treated in oxygen separator or deaerator 36 in order to remove any still remaining oxygen. The oxygen obtained in separator 36 is fed back to the recovering loop 38 via conduit 41. The pure water is discharged via outlet 43 from device 36. A partial flow of water from the oxygen separator 36 is returned to the burner 12 via return line 44, pump 46 and conduit 57.

In yet another embodiment as shown in Fig. 3, the water obtained in separator 36 - in addition to a control means for the reaction in burner 12- is advantageously used as a starting material in an electrolyser 40 for electrolysis of water into oxygen and hydrogen. Water from the separator 36 is extracted through the outlet 42 thereof and passed via return line 44, pump 46 to the inlet 48 of the electrolyser 40, while a partial flow thereof is passed through conduit 57 to the burner 12.

The DC current for the electrolysis can be suitably obtained from non-fossil resources, such as wind, solar and wave, generally indicated by 50. The outputs of oxygen 52 and hydrogen 54 of the electrolyser 40 are in fluid communication with the supply lines 14 and 16 respectively, which are also in fluid communication with oxygen buffer 18 and hydrogen buffer 20 via suitable valves (not shown).

In the invention the primary fluid loop of oxygen/hydrogen/steam/water is closed and fully separated from the working fluid circuit, so that contamination of the primary fluid is eliminated.

During start up ambient air is fed to the burner and hydrogen is combusted using this air. Then flue gas (steam and dissolved gasses) is discharged via a small start-up stack 29. For subsequent operation the air is gradually substituted by pure oxygen and the start-up stack is closed while the condenser 30 is taken in operation by means of suitable valves (not shown).

-6The presence of the separator 36 allows to remove contaminating gases from the water. If desired a further oxygen/nitrogen separator may be present in line 38 in order to split oxygen from air.

Claims (10)

CONCLUSIONS A system (10) for generating energy in a working fluid from hydrogen and oxygen, comprising a burner (12) for burning hydrogen and oxygen into steam, comprising an inlet (14) for oxygen and a inlet (16) for hydrogen, a boiler (22) operatively connected to the burner, for heating the working fluid with a supply (24) for introducing the working fluid and a discharge (26) for discharging heated working fluid and a heat exchanging surface (25) for heat exchange between the steam and the working fluid, a condensing steam condenser (30) operatively connected to the boiler downstream thereof, wherein at least one recirculation loop (32; 55, 57) is provided for recirculating reaction products of the combustion of hydrogen and oxygen downstream from the boiler to the burner, and a recovery loop (38) for recirculating excess oxygen separated in the condenser to the supply of z burner dust. The system of claim 1, wherein the recirculation loop (32) is arranged downstream of the boiler and upstream of the condenser to recirculate non-condensed steam to the burner. The system of claim 1 or 2, wherein the recirculation loop (55) is adapted to recycle condensate from the condenser to the burner. The system of any preceding claim, further comprising a separator (36) for separating oxygen from the condensate operatively connected to the condenser. The system of claim 4, wherein the recirculation loop (57) is arranged downstream of the separator to recycle oxygen depleted condensate from the separator to the burner. The system of any of claims 4 or 5, wherein the separator (36) includes a separated oxygen outlet (41) operatively connected to the oxygen recovery loop (38). The system of any preceding claim, further comprising an electrolysis device (40) for electrolysis of water in oxygen and hydrogen with a water supply (48) connected to the scale, and oxygen outlets (52, 54) and hydrogen, respectively, which are operatively connected to the respective supplies of the burner. The system of any preceding claim, further comprising an oxygen store (18) and a hydrogen store (20) operatively connected to the electrolyser outlets upstream of the burner. System according to any one of the preceding claims, wherein the oxygen reclaim loop (38) is connected to the inlet (37) of the burner (12). A system according to any preceding claim, wherein the electrolysis device (40) is electrically powered from a non-fossil source (50). The method of operating the system according to any of the preceding claims, wherein the oxygen and hydrogen flows are controlled such that combustion is performed at a stoichiometric excess of oxygen.