Patent Application
20100206171
This invention involves ship flue gas desulphurization technology method and system. It employs seawater to remove SO2 and other pollutant in ship exhaust. It relates to atmosphere environmental protection, ocean resources development and utilization, and prevention and control of shipping exhaust pollutant.
Shipping SO2 reduction problem is getting more serious and drawing people's attention worldwide as related legislation is getting strict and mature stage by stage. Shipping is an industry that correlates the global economy, in which a large amount of ships are fixed with fuel oil engines. Completely relying on using low-sulfur fuel oil may lead to dramatically rising cost. Hence providing shipping industry with economical flue gas desulphurization technology seems to be imperative.
Under mobile condition in different sea areas and with gas temperature as high as 200° C. to 490° C., compared to land fossil fuel fired industrial facility, the ship FGD technology must consider its practicality on economic cost concern. Instead, it requires the total cost of ship FGD facility including manufacture cost and running cost to be significantly lower than the total saving cost of using low-sulfur fuel for substitute.
As a result, the IMO (International Maritime Organization) brought out the ship desulphurization regulation in 2005. Soon, the potential economy advantage of seawater FGD technology was recognized. In 2007, a research carried by scholars from four well known universities concluded that using the ocean resource, that is, the seawater, to realize ship SO2 reduction is an expectation that people pursued but have not realized in a long period. For details, please refer to a report by the Alliance for Global Sustainability of four universities (Massachusetts Institute of Technology, University of Tokyo, Chalmers University of Technology, and Swiss Federal Institute of Technology Zurich), titled, ‘Seawater Scrubbing—reduction of SOx emissions from ship exhausts’ ISBN: 978-91-976534-1-1).
Some of the existing technologies that apply seawater scrubbing method to reduce ship exhaust are described below.
One method uses a hollow fiber contactor as scrubber, and in this scrubber the ship exhaust after dust removal is scrubbed with seawater. The process is monitored by control system that is formed by SO2 consistency sensor, water quality sensor, and PLC programming controller. The system may monitor and record the real-time SO2 consistency in processed ship exhaust, monitor and record discharged water quality, and control the water discharging respectively. Please refer to ‘A seawater scrubbing ship exhausts processing method’ (Patent number 200710012371.1, published in China, Jan. 16, 2008).
This technology has some problems.
Firstly, the technology uses a hollow fiber contactor as scrubber. This hollow fiber contactor only tolerates decades of centigrade. It can not be used for high-temperature gas, especially for the ship engine exhaust with temperature as high as 200-490° C.
Secondly, pressure drop and resistance are very high when the hollow fiber contactor is used for scrubbing. Operation cost and energy expenditure would be quite high if additional booster fan is installed.
Another technology is described at ‘Seawater Scrubbing—reduction of SOx emissions from ship exhausts’ (ISBN: 978-91-976534-1-1, American, 2007). This reference recites: ‘It is shown that seawater scrubbing is a promising technology for reducing sulphur oxide emissions from ships. Based on a 12 MW engine burning fuel with a 3% sulphur content. Calculations have been made for different efficiencies of sulphur scrubbing, different water temperatures, and for six different water types. The results of the calculations give the volumes of water required for (i) uptake of SOx (the scrubbing process), (ii) dilution of the scrubbing water to achieve a pH of 6.5, (iii) further dilution to achieve a pH within 0.2 units of that in the ambient water, and no more that a 1% reduction in dissolved oxygen concentration. The volumes of water required for a given efficiency of the scrubbing process . . . would require significantly larger water volumes for scrubbing and dilution . . . would therefore require detailed case studies. It may be possible to reduce the volumes of dilution water required by, for example, aeration of the scrubbing water and addition of base to neutralise the acidic sulphur oxides. Further studies would be needed in order to assess these options.’
The research is representative one in the seawater scrubbing method field for marine ship SO2 reduction. However, it remains in the stage of principle. It still fails to solve some problems: low absorbing efficiency, large diluting water volume. To prevent environmental pollution from discharge water pollutant, EPA and IMO have passed regulations about the blending of discharge water with surrounding seawater: The blending process is defined as quick blending area and slow blending area. The boundary pH value is 6.5 for quick blending area, and 15 minutes is the time limitation for this value to reach. For the slow blending area, the difference of boundary pH value and surrounding seawater pH value must less than 0.2. The report is based on a 12 MW engine burning fuel system. In order to fulfill the requirements about gas and discharge water, the ship must prepare thousands of tons of seawater per hour. Seawater needs further dilution after being discharged out of ship and require further blending with surrounding seawater that not less than 40000 times of its volume.
This research has not mentioned application of both technology and facility design.
A third technology was described at Ecosilencer Exhaust Gas Cleaning Presentation (February 2006, Canada). This presentation introduced EcoSilencer method seawater scrubbing system and equipment (
The high-temperature gas from engine must be cooled so that SO2 can be absorbed. For this reason, the scrubber of U.S. Pat. No. 7,056,367 adopts ‘exhaust gas inlet to liquid scrubbing tank’, that is, the bubbling scrubbing method. However, the high-temperature gas cooling process and scrubbing process are carried in the same tank at the same time. Hence, the transfer efficiency is quite low. In addition, the two processes conflict with each other. In order to increase scrubbing efficiency under such condition, the only way is to add scrubbing water volume and pressure loss, and it subsequently causes significant energy consumption and running cost. It seems that the problems of the seawater scrubbing system and device that adopt this scrubber have to accept the conflict of cooling the high-temperature gas and absorbing SO2 at low-temperature, as well as the conflict of the scrubbing effect and cost reducing.
In conclusion, existing research and experimental technology must confront with similar issues when it comes into the practical field.
With the existing technologies, it is difficult to meet the environmental requirements about gas exhaust and seawater discharge under acceptable cost. Presently, energy consumption and running cost are both very high to meet discharging water regulation because of the large volume of scrubbing water and diluting water. The cost will increase if higher requirements for discharging water are published in the future.
Also, the existing technologies are unsuitable for the mobile nature of a ship. Different sea area and controlling area have different environment condition and control requirement. Condition changes consistently for marine ship sail between different sea areas and controlling area, for example: seawater quality, sulphur content in different batches of fuel, discharging regulation in different environments, and other circumstances. It appears that flue gas desulphurization technologies with fixed parameters can not be applied for ships.
Apparently, the expectation that using marine resource to eliminate air pollutant will not be realized if the above mentioned problems remain unsolved.
To comply with the laws and regulations about the ship desulphurization issue, practical ship SO2 reduction method and systems using seawater must be brought out so that the expectation that making use of the marine resources to eliminate ship atmospheric pollution can be realized.
A first aspect of this invention is to overcome the shortcomings of existing ship flue gas desulphurization (FGD) methods, and to provide a ship gas desulphurization method which offers high desulphurization efficiency, consumes less scrubbing and diluting seawater volume, expends low energy and cost, and has the ability to adapt in different sea areas and controlling areas.
A second purpose of this invention is to overcome shortcomings of existing ship gas desulphurization facilities, and to provide a ship gas desulphurization system which offers high desulphurization efficiency, consumes less scrubbing and diluting seawater volume, costs less for manufacturing and running, has small volume, is durable, and is suitable for ships which have limited usable space and large sailing area.
In one embodiment, a FGD method comprises the following steps:
A) cooling followed by scrubbing high-temperature flue gas containing SO2 from ship engine, wherein said scrubbing is done with seawater in a scrubber, and discharging the scrubbed clean gas;
B) transferring acidic seawater formed during the scrubbing process due to the absorption of SO2 to a water-saving deacidification device;
C) blending acidic seawater in the water-saving deacidification device with alkaline seawater, making mixed seawater, and aerating the mixed seawater; and
D) discharging the seawater after deacidification once the seawater is deemed suitable for discharging into the sea.
The said scrubbing step uses seawater in the scrubber, where scrubbing in done in the scrubber at a packing scrubbing section.
The said deacidification of this ship FGD method includes blending alkaline seawater into the water-saving deacidification device, wherein a flow of the alkaline seawater is regulated by a first regulator that regulates the flow by opening adjustable valves and/or output adjustable pumps; and wherein a flow of air that blown into the water-saving deacidification device in the aeration process is regulated by a second regulator that regulates the flow by opening adjustable valves, dampers and/or adjustable fans.
In the said scrubbing step of this ship FGD method, the flow of scrubbing seawater is regulated by a regulating means. The said regulating means regulates the flow by opening adjustable valves and/or output adjustable pumps.
The said regulating of this ship FGD method employs means to regulate flue gas emission and seawater discharge according to environmental requirements of the sailing area of ship. The regulating is done by manual work and/or a desulphurization controller.
There may be an impurity separating process between scrubbing and deacidification. The separating process means first separates impurities by a separator and then discharges through waste outlet.
An FGD system according to this invention comprises a scrubber and a water-saving deacidification device. Upper part of said scrubber comprises a packing scrubbing section and is connected with scrubbing seawater pump by pipelines; lower part of the scrubber is the cooling section. One end of the scrubber links ship engine smoke pipe by a scrubbing inlet pipe and the other end links scrub outlet pipe. The water-save acid removal device lies below the scrubber and is connected with it. The water-saving deacidification device connects with blending seawater pump, fan, and total drain pipe to discharge post-deacidification seawater that is suitable for discharge.
In one embodiment of the ship FGD system, there exists a blending alkaline seawater passage on the said water-saving deacidification device, at which an alkaline seawater flow regulator is installed. The flow regulator is selected from an opening adjustable valve or/and an output adjustable pump. The said water-saving deacidification device may also comprise an air inlet passage, at which an air flow regulator is installed. The air flow regulator is selected from an opening adjustable valve, dampers or/and an output adjustable fan.
In an embodiment of the ship FGD system, there exists a scrubbing seawater passage on the said scrubber, at which scrubbing seawater flow regulator selected from an opening adjustable valve or/and output adjustable pump are installed.
The valve, dampers may comprise levers; the pump and fan may comprise electrical speed governor; the said lever and electrical speed governor may be coupled to a desulphurization controller.
In one embodiment, the said scrubber comprises a shell (3.1), a cooling section, packing scrubbing section, and a water tank, wherein the cooling section is situated under packing scrubbing section.
Further, the ship FGD system may include an impurity separator installed between scrubber and water-saving deacidification device.
In one embodiment of the FGD system, the desulphurization controller comprises of commanding apparatus, sensor, central processing unit (CPU), actuator, and global sea area position system.
Persons skilled in the art will appreciate that the invention is not limited by the embodiments disclosed above, and further embodiments are possible without departing from the scope of the present invention.
The accompanying drawings, which are incorporated in and constitute a part of this specification, exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the invention. The drawings are intended to illustrate major features of the exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale.
Name of components or structures corresponding to the figure number are:
Technical principle and overall effect of the ship FGD method and ship FGD system of this invention are described below.
Technical principle: Main functions of the ship FGD method and system, as well as problems for them to solve comprise: scrubbing and absorbing, water discharging, and mobile sailing.
1) Scrubbing and absorbing: Seawater scrubbing is employed in order to remove SO2 and other pollutant in ship exhaust that are expelled from engine. Seawater has strong dissolving and absorbing ability for SO2 because of its physical and chemical characteristics, At the same time, seawater can scrub and absorb nitrogen oxide and particulate well. Ships typically have a limited usable space, consequently the FGD system has to be small sized. This helps the process to take less time than larger system; hence the said scrubbing and absorbing must be completed in a very short time. It means the FGD system not only must possess very high total absorbing efficiency, but also have very high absorbing speed and the scrubbing must be extremely efficient and effective. For the above reasons, the powerful dissolving and absorbing quality of seawater must be coordinated with a powerful transfer process which passes the pollutants from flue gas to the liquid seawater. On the other hand, temperature of diesel motor exhaust could be as high as 490° C. Both for SO2 removal or for system protection, the high-temperature flue gas must to be cooled before entering the scrubbing step. To address this, the scrubbing process of this invention employs a counter-flow packing scrubber. The highly efficient ship FGD method and system disclosed in this invention make scrubbing and cooling to take place at different times, using seawater as scrubbing material. The functional section of the scrubber comprises filling section. The scrubbing seawater is distributed to the filling material evenly by a water distributor from upside; the high-temperature gas is cooled and then passes the filling material starting from a bottom end and going upwards; the scrubbing seawater, on the other hand, passes the filling material starting from the top, and going downwards. Because of the huge surface area formed by fillings, gas and liquid are provided with a huge contact area; hence transferring ability and absorbing ability are very powerful. An aim of this invention is to achieve highly efficient desulphurization. The filling method can significantly reduce resistance for the passing gas to realize high scrubbing absorbing quality and low running cost.
2) Water discharging: Seawater which is used for scrubbing has dissolved SO2 and is acidic, and it has to be discharged into the ocean after pH raising treatment. Existing technologies employ simple dilution method which consumes large diluting water volume and causes high energy consumption and cost. To overcome these shortcomings, this invention introduces water-saving deacidification device to decrease diluting water volume. SO2 dissolves in scrubbing seawater and turns to SO32− and other acidic materials; they then turn to carbonic acid and other acid materials when fresh alkaline seawater is blended in. A conventional diluting process requires huge volume of diluting water because the pH value rises slowly. In the water-saving deacidification device of this invention, fresh alkaline seawater is blended in simultaneously with air. This makes the carbonic acid volatile quickly and the pH value of scrubbing seawater rises rapidly, so the volume of diluting water reduces much.
3) Mobile adjustment. Marine ship regularly sails in different sea areas, thus, it faces changing conditions such as seawater quality in different sea areas, sulphur content of different batches of fuel, discharging regulation in different environments. Therefore, technologies with fixed parameters cannot be employed on marine ship. This invention adjusts scrubbing seawater flow, blending seawater flow to the water-saving deacidification device, and air flow to the water-saving deacidification device. It also uses controller including CPU to monitor the above described adjustments. Thus, the FGD method and system of this invention are very applicable for marine ship which always moves.
FGD method and system of this invention conform to environmental protection laws and regulations. Technical advantages offered by the methods and systems of the present invention are significant.
Firstly, the methods and systems are highly efficient in pollutant reduction. It can reduce 99% oxysulfide, 20% oxynitride, and 80% particle. It has important significance to international shipping business for the environmental objectives. IMO published restrictions for SECA (SOx Emission Control Area) that the sulphur content of fuel oil used on board ships must not exceed 1.5%. Alternatively, ships must fit an exhaust gas cleaning system to make the sulphur content of exhaust emissions equal to it when ships use fuel oil with sulphur content not exceed 1.5%, that is, the ‘desulphurize equivalent fuel oil sulphur content’ must not exceed 1.5%. Other international organizations are pursuing a 0.1% fuel oil sulphur content goal. Currently, global average sulphur content of heavy oil is approximately 3%, so the scrubbing efficiency must be 50% to reach the desulphurized equivalent fuel oil sulphur content 1.5% goal, and 96.7% to reach the desulphurized equivalent fuel oil sulphur content 0.1% goal.
Secondly, the systems and method of the present invention demonstrate that they can offer excellent desulphurization result and environmental protection performance when moving between different sea area where the seawater quality, fuel sulphur content, and environmental restriction vary constantly.
Thirdly, the discharged water of this invention is environmental friendly. As mentioned previously, the EPA and the IMO regulate that ships discharge water must make the boundary pH value to reach 6.5 for quick blending area within 15 minutes. Method and system of this invention enable the pH value of discharge water to reach 6.5 before discharge; as a result, the quick blending area is not even needed. The harmful effect to the ocean for 15 minutes is eliminated completely at the very first step. On the other hand, the diluting rate in slow blending area can be decreased to 1:2000 from 1:40000. Compared to existing technologies, merely 1/20 surrounding seawater is needed to blend. Slow blending area reduces significantly and the discharged water produces much more environmentally friendly quality.
Fourthly, it decreases the manufacture and running costs evidently by many ways, including reducing the running energy and seawater volume; it produces outstanding economic result that the total cost is significantly lower than the cost of using low sulphur fuel.
Applications:
Further description of the ship FGD methods and systems by figures and examples is given below.
A: Examples of Ship FGD Method
As shown in the embodiment illustrated in
a. Scrubbing: Cool and then scrub the high-temperature flue gas that contains SO2 from ship engine, and discharge the scrubbed clean gas after scrubbing. The said scrubbing step uses seawater in the scrubber.
b. Acidic seawater transfer: Transfer acidic seawater formed in the scrubbing process which absorbs SO2 to water-saving deacidification device;
c. Deacidification: Blend acidic seawater in the water-saving deacidification device with alkaline seawater, make mixed seawater, and aerate the mixed seawater;
d. Discharge: Discharge the seawater after deacidification that is suitable for discharge into the sea; The said scrubbing step using seawater in the scrubber means scrubbing in the scrubber with packing scrubbing section.
In order to adapt changing conditions as marine ship usually sails between different sea area, for example seawater quality, sulphur content of different batches of fuel, discharging regulation in different countries and areas, the deacidification process uses water-saving acid removal device to blend alkaline seawater in. The alkaline seawater flow is regulated by regulator; the said regulating is carried by output adjustable pumps, or opening adjustable valves, or the combination of output adjustable pumps and opening adjustable valves. Air blown into the mixed seawater in the water-saving deacidification device is regulated by regulator; the said regulating is carried by output adjustable fan, or opening adjustable valves or dampers, or the combination of valves and fans, or the combination of dampers and fans. The scrubbing seawater flow in the scrubbing process is regulated by regulator; the said regulating is carried by output adjustable pumps, or opening adjustable valves, or the combination of opening adjustable valves and output adjustable pumps; the said regulating is controlled by the desulphurization controller according to different environmental requirements in different sea area for exhaust emission and seawater discharging; manual work regulating is another application example. There may exist an impurity separation step between scrub and deacidification process; the separating process means first separate impurities by a separator and then discharge through waste outlet.
The example shows a ship with 12MW diesel fuel engine, exhaust gas 200-490° C., exhaust volume approximately 67,095 Nm3/h; Under the 3% fuel oil sulphur content condition, adopting desulphurization method of this invention enable the desulphurized equivalent fuel oil sulphur content to reach 0.1%, and the discharging water pH≧6.5. The seawater consumption in different sea areas:
the Baltic Sea scrubbing seawater 300 m3/h blending seawater 1100 m3/h
the North Sea scrubbing seawater 280 m3/h blending seawater 950 m3/h
The Example embodiment of
This example is applied on large tonnage ships which with 60MW diesel fuel engine, exhaust gas 200-430° C., exhaust volume approximately 310,100 Nm3/h; Under the 3% fuel oil sulphur content condition, adopting desulphurization method of this invention enable the desulphurized equivalent fuel oil sulphur content to fulfill SECA standard (2005), that is 1.5%, and the discharging water pH≧6.5. The seawater consumption in different sea areas:
the Baltic Sea scrubbing seawater 980 m3/h blending seawater 3600 m3/h
the North Sea scrubbing seawater 880 m3/h blending seawater 2600 m3/h
B: Examples of ship FGD system:
The protection range of this invention is not limited by examples above. It should be understood that processes and techniques described herein are not inherently related to any particular apparatus and may be implemented by any suitable combination of components. Further, various types of general purpose devices may be used in accordance with the teachings described herein. The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations will be suitable for practicing the present invention.
Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. Various aspects and/or components of the described embodiments may be used singly or in any combination. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CN08/71307 | 6/13/2008 | WO | 00 | 4/5/2010 |
