FIND RASMUS (DK)
| WO2004065869A1 | 2004-08-05 | |||
| WO1999067102A1 | 1999-12-29 |
| US4205529A | 1980-06-03 | |||
| US4942734A | 1990-07-24 | |||
| GB2283284A | 1995-05-03 | |||
| EP1889658A2 | 2008-02-20 |
| P A T E N T C L A I M S
1. A method for recovery of heat originating from a CO 2 recovery process wherein an absorption or adsorption chiller regenerator step is inserted and wherein said chiller step is inserted at a point where the thermal energy of the stream entering the chiller is higher than the thermal energy needed in the process step downstream from the chiller and/or that the stream is able to release thermal energy at a temperature of at least 40°C.
2. A method according to claim 1, wherein heat is supplied and utilized for stripping in a chemical or physical absorption process.
3. A method according to claim 1, wherein at least one chiller step is inserted before step a) and/or between steps a) and b) and/or after step d) in the process comprising at least the steps of a) feeding a gas (Gl) comprising carbon dioxide into a boiler (A2) providing a colder gas (G4); b) feeding the gas (G4) into an absorption column (A5); c) absorbing the gas (G4) in an absorbing agent, by which the gas (G4) is separated into a carbon dioxide-lean gas (G5) and a carbon dioxide-rich liquid (L2); and d) separating the liquid (L2) obtained into a carbon dioxide-rich stripper off gas (G6) and a carbon dioxide-depleted liquid (L3) by means of stripping in a stripper column (A6).
4. Use of an adsorption or absorption chiller regenerator in a CO2 recovery plant for generating a cooled liquid, which cooled liquid is not part of the CO2 recovery plant.
5. Use according to claim 4, wherein the liquid is for consumption or for use in an air conditioner. |
Method for recovery of heat from a carbon dioxide recovery process.
The present invention relates to a method for recovery of heat from recovery of carbon dioxide from gaseous sources. More particular, the invention relates to a method for recovery of heat where carbon dioxide is recovered in a chemical or physical absorption process where heat is added for stripping purpose. The present invention also relates to the use of an adsorption or absorption chiller unit in a CO 2 recovery plant for generating a cooled liquid.
Background of the invention
CO 2 recovery plants are widely used to clean and/or recover CO 2 released from combustion of hydrocarbons. Such plants often comprise an absorption step using a chemical or physical absorber followed by a stripping step wherein the CO 2 gas and the absorbent are separated into a CO 2 rich gas and the liquid absorbent, which is reintroduced into the absorber. The separation in the stripper is facilitated by heat eventually originating from the combustion of hydrocarbons, such as oil, coal or natural gas. The warm CO 2 gas leaving the stripper is cooled and either discarded or subjected to further downstream purification steps if intended for use in e.g. the food and beverage industry or EOR.
Most often the heat supplied as the hot CO 2 gas exceeds the energy needed in a downstream process e.g. a stripper. This thermal en- ergy released from the cooling of the CO 2 gas leaving the stripper is usually wasted or utilized for central heating purposes. However, such utilization of the thermal energy will always be accompanied with a loss of energy which cannot be exploited elsewhere. Additionally, the demand for central heating varies with the seasons thus it would be desirable to find a feasible utility of the energy that could substitute and/or complement central heating. Therefore, there is still a need for improving existing CO 2 recovery plants by finding new ways of optimizing the use of the excess energy from the plants. Therefore, an object of the present invention is to improve existing CO 2 recovery plants by utilizing the excess
heat derived there from in a more valuable process than e.g. central heating.
Summary of the invention Accordingly, an object of the present invention is to recover heat from CO 2 recovery processes, more particular to recover heat from CO2 recovery processes in which heat is utilized for stripping a chemical absorption process.
The recovered heat is utilized for the generation of cold liquid in an absorption chiller unit using an absorption chiller unit by adding heat to the regenerator.
Hence in a first aspect the present invention provides a method for recovery of heat originating from a CO 2 recovering process wherein an absorption or adsorption chiller regenerator step is inserted at a point where the thermal energy of the stream entering the chiller is higher than the thermal energy needed in the step downstream from the chiller and/or that the stream is able to release thermal energy at a temperature of at least 40°C. The temperature is most preferable down to 40°C, but if economically feasible lower temperatures may be employed. In a second aspect the present invention relates to the use of an adsorption or absorption chiller unit in a CO 2 recovery plant for generating a cooled liquid, which cooled liquid is not part of the CO2 recovery plant.
When CO2 is generated by combustion of hydrocarbons huge amounts of thermal energy is supplied in the form of a hot CO2 containing gas stream generated from the combustion of hydrocarbons. This gas is cooled in order to render it suitable for purification as required for release or recovery. The heat obtained from the cooling of the gaseous stream is most often fed to a stripper. However, the thermal energy generated from the cooling of the gaseous stream exceeds by far the thermal energy needed to strip e.g. an absorber liquid comprising CO2. Hence, by introducing an absorber/adsorber chiller regenerator at any point, at which the thermal energy of the stream supplied to the chiller supplied exceeds the thermal energy required in a down stream unit op-
eration, for example a unit immediately downstream from the chiller, thermal energy is extracted from the stream. Thereby is provided for both thermal energy for e.g. stripping and thermal energy to be utilized in an absorption chiller unit to cool a liquid, in particular water. The stream leaving the regenerator should most preferably be as low as 40°C. I.e. the stream must be able to release thermal energy at a temperature of at least 40°C.
The stream leaving the regenerator is subsequently fed as a hot reservoir to a heat exchanger. In the heat exchanger the energy of the hot reservoir is transferred to a cold reservoir. A temperature difference between the hot and cold reservoirs must be at least 15°C in order to achieve a reasonable Carnot efficiency.
If for example, the chiller unit is based on LiBr technology where LiBr is the absorber and water the refrigerant, the system is typi- cally operated at 65°C. Hence the hot reservoir should preferably be 80°C and the cold reservoir at the most 50°C in order for the process to be feasible. The choice of refrigerant technology may depend on the ambient temperatures. Other systems are based on NH4 and water in which case NH4 is th erefrigerant and water the absorbent. Such systems are capable of operating at lower temperatures.
The present invention is particular suitable for plants where there is a combined need for recovering pure CO 2 and cooling a liquid/fluid which is not an integral part of the CO2 recovery process.
Hence the present invention utilizes excess energy form one process in another separate process that would else wise require an additional energy supply.
By incorporating the adsorption or absorption chilling regenerator into such a CO 2 recovery plant excess heat, normally discarded e.g. in a cooler, is lead to a chiller unit in which a liquid, such as water, can be cooled. Thus, by incorporating this absorption/adsorption chiller step the excess thermal energy is converted and utilized as the energy source of a more valuable character, e.g. to save electricity utilized for running a refrigeration compressor based chiller, compared to the prior art plants, where the thermal energy is typically discarded to a cooling
tower or air cooler.
Such method and application is particular useful in the beverage industry where provisions are already present for recovery of particularly high purity CO 2 . Incorporating a chiller unit according to the present in- vention in such a CO 2 recovery plant provides energy for another essential process namely cooling means for the water used in the beverages, e.g. soft drinks, requiring a certain low temperature, e.g. 7°C.
In a particular embodiment the heat is recovered from a process where heat is used to strip a chemical/physical absorbent used in a CO 2 recovery plant, excess heat is led to a chiller unit in which a liquid is cooled to a desired temperature.
In another particular embodiment is provided a method wherein the chiller step is inserted before step a) and/or between steps a) and b) and/or after step d) in the process of a) feeding a gas (Gl) comprising carbon dioxide into a boiler
(A2) providing a colder gas (G4); b) feeding the gas (G4) into an absorption column (A5); c) absorbing the gas (G4) in an absorbing agent, by which the gas (G4) is separated into a carbon dioxide-lean gas (G5) and a carbon dioxide-rich liquid (L2); and d) separating the liquid (L2) obtained into a carbon dioxide-rich stripper off gas (G6) and a carbon dioxide-depleted liquid (L3) by means of stripping in a stripper column (A6).
The particular process described above is the most frequently used process in a high purity CO 2 plant, optionally further comprising a flash step between the absorber and the stripper, in particular when the gaseous source comprises NOx's, sulphurous compounds and/or volatile organic compounds. The particular method above is particular useful in the consumers industry, such as beverages, e.g. soft drinks and beer, where there is both a need for high purity food grade CC^ and a need for cooling water. Thus, according to the present invention the CO 2 plant often already present may be improved by incorporating the inventive adsorber/absorber chiller regenerator at a suitable point of the process,
Detailed description of the invention
The source from which CO2 is to be recovered may be any CO2 containing gas, but presently flue gas is the most preferred gaseous CO 2 source. The present invention is related but not limited to a process as depicted in figure 1 where a self-generating CO 2 -plant is used as an example.
Another possible setup is a traditional CO 2 recovery plant. Still other setups are possible and this invention relates to the recovery of heat added to or generated from a CO 2 process in general. As such the absorption/adsorption chiller could also be implemented in other hot streams but a gaseous CO 2 source.
In the context of the present invention the chiller may equally be an adsorption or absorption chiller regenerator. The absorption/adsorption chiller regenerator is preferably incorporated in the actual plant but may also be positioned at a distance there from provided the stream can be transported in a practical way thereto. For example, a power plant having a CO 2 recovery plant may supply heat to a chiller unit in connection with the plant itself or con- nected to a neighbouring factory demanding means for cooling fluids. In a specific embodiment the CO 2 recovery plant is located in a factory producing beverages, which also requires cooling of liquid to said beverages.
Referring to figure 1 the present invention will now be explained in greater details with reference to this embodiment.
Flue gas is generated by combustion of hydrocarbons in burner Al to generate a hot CO 2 -containing gas stream Gl. The gas stream Gl is cooled in a boiler A2 to generate a colder gas stream G2. This gas stream is then cooled by means of a direct contact cooler A3, to gener- ate a gas stream G3, which has a temperature close to the water dew point temperature. The gas stream G3 is compressed by blower A4 to generate a gas stream G4, which is sent to an absorption column A5. In A5 the gas stream G4 is washed by means of a CO 2 -lean MEA/water- solution Ll, which by means of a chemical reaction will absorb the CO 2
present in gas stream G4 to generate a CO 2 -rich liquid L2 and a CO 2 free gas G5. The CO 2 -TiCh liquid L2 is pumped to a stripping column A6 where the CO 2 in the CO 2 -TiCh liquid L2 is stripped off by means of heat generated in boiler A2 in order to produce a CO 2 -HCh gas stream G6 and a C0 2 -lean liquid L3. L3 will upon heat transfer be the liquid Ll used for the absorption step in A5.
The CO 2 -HCh gas stream G6 also containing steam is then being cooled in the absorption/adsorption chiller regenerator A7 to recover most of the heat, which is needed for running an absorption/adsorption chiller unit to produce a cold chilled liquid L5 from liquid L4, which is an externally supplied liquid not being part of the CO 2 recovery process, the liquid L5 can be exported to consumers. Said liquid may in a particular embodiment be water for use in the beverage industry, e.g. for use in soft drinks or beer. In yet another embodiment the liquid may be water for use in an air conditioner apparatus or in general any where a cooling application is needed.
In the embodied example the chiller A7 is located downstream from the stripper. In another embodiment the chiller may be situated upstream from the boiler A2 or after the boiler A2. It is also contem- plated that more than one chiller A7 can be used at different locations provided the stream is warm enough to provide both heat to the unit operation of the CO 2 recovery plant and heat/thermal energy to the chiller. By introducing the absorption chiller regenerator, A7, approximately 70% of the heat normally removed in heat exchanger A8 can be recovered to run an absorption chiller unit. Hence by incorporating the chiller at certain stages of the CO 2 recovery process thermal energy not used at all or used in a non-optimal way may be exploited in a chiller unit whereby substantial amounts of energy in form of electricity is saved. It is further contemplated that the present invention relates to a plant comprising a CO 2 recovery unit and an adsorption/absorption unit. Said CO 2 recovery unit comprises at least starting upstream a boiler, optionally a direct contact cooler, an absorber, optionally a flash column, a stripper and optional further down stream purification units such as a
washer, a dehydrator and a condenser. Usual unit such as pumps, blowers etc. are ubiquitous and the skilled will readily recognised where these standard units are employed. The adsorption/absorption unit comprises at least an absorption/adsorption chiller regenerator, and optionally a heat exchanger, condenser, evaporator, adsorber, and absorber depending on the choice of chiller used.
All units mentioned may be those normally used in the art.
Example A typical CO 2 recovery plant produces 1000 kg CCVhr from combustion of natural gas. In the process 5000 kWh thermal power will be generated in boiler A2.
In the prior art plants 4550 kWh of the 5000 kWh generated in A2 is removed in heat exchanger A8. However, by introducing the ab- sorption/adsorption chiller regenerator A7 according to the present invention it is possible to recover more than 3500 kWh for running the absorption chiller unit.
For example, based on LiBr solution technology known in the art it is possible to recover more than 80 % of the recovered heat from the CO2 plant, i.e. the 3500 kWh, to produce 2800 kWh water chilled by cooling liquid stream L4 from 14°C to liquid stream L5 having a temperature of 7°C.
In normal operation, a chiller based on a refrigeration compressor will normally consume approximately 20 kWh electrical power to produce 100 kWh of 7°C cold water. Hence for this example the electrical power savings would be 3500 kWh * 20/100 = 700 kWh electrical power.