GR1009967B - Method of converting an existing ship' s chimney to an exhaust desulphurisation system - Google Patents

Abstract

The invention relates to a method destined to convert an existing ship’s chimney into an exhaust gas desulphurization system. Said method is characterized by the use of thermal spraying inside the chimney of the main engine to create an anti-corrosion liner, the installation of rows of water spraying nozzles, the creation of a chamber for the collection of the exhaust produced by the main engine and the electromotors and a washing water inlet and outlet arrangement. Scrubbers are well known in shipping and are used to reduce the level of sulfur oxides derived from exhaust gases coming from internal combustion units, in order to comply with existing and upcoming regulations for reduced emissions of sulfur oxides into the atmosphere. The main advantage of the present invention is that it uses the existing chimney by converting it into a desulphurization system so that the cost of equipment as well as the cost and time for installation on board are dramatically reduced ; implementation is allowed with the ship remaining in normal operation without the need to be transported to the shipyard.

Description

Description

Method of converting an existing ship chimney into a flue gas desulfurization system

The present invention refers to a method of converting the existing smokestack of a ship into an exhaust gas desulphurization system, with the aim of reducing the emissions of sulfur oxides (SOx) from the internal combustion engines of a ship.

Exhaust gas desulphurisation systems are already being used in shipping to achieve a reduction in the level of sulfur oxides from the exhaust gases coming from a ship's propulsion and electrical engines in order to meet existing and upcoming regulations regarding reduced emissions of sulfur oxides into the atmosphere . Such systems consist of an absorption column, usually metallic, cylindrical or rectangular in cross-section, placed inside the ship and acting as an exhaust gas scrubber with wash water - either in a packed arrangement, or by direct water injection, so that the alkalinity of the wash water, to bind sulfur oxides. The wash water is then discharged into the sea.

These special structures - exhaust gas desulfurizers (SOx scrubbers) - are usually made of special materials to withstand the increased temperature of the exhaust gases, the high acidity resulting from the sulfur oxides bound by the washing water and the high salinity, when the marine water is used as rinse water. Exhaust gas desulphurisation systems consist of large structures or absorption columns, which must be connected to the ship's chimney, either in series or parallel, in the existing arrangement, which requires time-consuming and significant work to install the desulphurisation units in the existing layout of the ship. Such works relate to the removal of the ship's existing ironwork, piping and flue gas equipment, relocation of existing equipment, as well as additional ironwork to accommodate the installation of new equipment. These extensive works require the ship to be decommissioned and transferred to a shipyard to carry out the above works, as well as the ship being docked to carry out work below the ship's waterline, such as the installation of a seawater intake to the system desulfurization, and the discharge of leachate into the sea.

Our method is innovative as it uses the existing ship's main engine exhaust stack, converting it into an exhaust gas desulphurization system by applying corrosion protection and adding the required equipment. The main advantage of the present invention is the reduced intervention on the ship, compared to the work required for the installation of a special construction of large dimensions scrubber of the market. Therefore, in contrast to the systems in circulation, the present invention excels in terms of the significant simplification of the equipment required, the drastic reduction of the volume and weight of the equipment and the reduced installation work required, as the installation can be done in a short period of time, without requiring the ship to attend a shipyard for tanking, with the end result of an exhaust gas desulphurization system at significantly reduced cost and time.

The method and its application are understood from the following description. According to our method, exhaust gas cleaning is carried out using direct water spray, through nozzles, which are installed in multiple rows and distributed along the existing exhaust chimney of the main engine, calculated to allow the necessary reaction time of the of water with the exhaust gases. Because the method uses the existing stack of the main engine and thus is not constrained by the limited spatial layout of a conventional scrubber, it has the advantage that the cleaning and desulfurization of the exhaust gases takes place along the entire stack and provides ample space for an efficient reaction of of water with the exhaust gases. According to the method, the use of different series of spray nozzles allows control of the droplet size which is critical for an effective cleaning process.

Flushing water is collected in the lower sections of the modified chimney in conjunction with a suitable deflector of the flue gas flow of the existing flue - either concentrically or eccentrically to the existing flue - without further restrictions, meaning that the back pressure on the flue gas flow is minimal. The washing water is collected in the collection tank, which is formed in the lower part of the chimney.

A key aspect of the present method is the corrosion protection used on the metal surfaces of the chimney. The existing smokestack of a ship's main engine in use is usually made of carbon steel which is not suitable for handling corrosive fluids with high salinity and high acidity characteristics, especially in combination with elevated temperatures. According to our method, all existing metals, in contact with corrosive fluids, are protected by applying corrosion-resistant coatings, using thermal spray technologies. Thermal spray techniques are coating application methods in which metal surfaces are sprayed with molten or heated materials. Thermal spraying can provide thick coatings, from 20 microns to several millimeters, depending on the process and material, over a large area, at a high deposition rate. In the present method, the coating materials used are based on mainly nickel-molybdenum-chromium alloys, applied via high velocity flame spray (HVOF) or high velocity air fuel (HVAF) techniques. Coating will be done over the entire surface of the existing chimney, including the supports and fittings that are installed. Thermal spraying can be done robotically or manually, with skilled personnel moving over supports and platforms installed inside the existing chimney in advance, or via a personnel lift specially configured for temporary placement inside the chimney. The dimensions of the chimney of the main engine of large ships usually range in diameter from 1200 mm to 2600 mm, thus allowing the work required to install the system to be carried out.

In addition, the device of the present invention functions as a multi-inlet exhaust gas cleaning unit, thus allowing the parallel connections of the ship's electric engines, in the same chimney of the main engine.

The present method provides for a device in which the flue gases heading towards the existing chimney are temporarily diverted through specially designed ports outside the vertical direction, during which the washing water descends, which is collected in a suitably designed collection container, from where it is drained into a pipe that ends on the reefs of the ship. The exhaust gases, rising up the chimney, go to the diversion chamber and after bypassing the water collection and drainage container, they continue their journey meeting the water sprayed by the arrays of nozzles. The exhaust gas collection and diversion chamber described above also functions as an exhaust gas collector, as the exhaust pipes of the ship's auxiliary engines are connected to this point. In this way, all exhaust gases are directed to the specially designed chimney, where desulphurization takes place through the water sprayed from the arrays of nozzles along the entire length of the chimney. All exhaust gases are cooled by direct cooling which is carried out by the first rows of spray nozzle arrays and is calculated to cool the exhaust gases and allow the capture of sulfur oxides but also to increase the density of the exhaust gases. The first, lower array of spray nozzles will have the function of cooling the exhaust gases - by spraying water in the direction of the exhaust gas flow, and will include nozzles with an obtuse cone type spray profile and the production of extremely small droplet sizes suitable for cooling the exhaust gases through evaporation. The second lower array, from the lowest spray nozzle array, will have the function of smoothing the exhaust gas flow and will include nozzles with an acute-angle cone-type spray profile with water spray in the direction of the exhaust gas flow. The following nozzle arrays are alternated with spray nozzles of different sizes with a spray direction opposite to the exhaust gas flow to produce a suitable and controlled droplet size distribution. The size of each nozzle array is such that it can be inserted into the existing chimney.

In the upper part of the described flue gas desulphurization system, a mist eliminator is installed, consisting of corrugated sheets in order to trap water droplets carried by the flue gas stream. A nozzle array is located above said droplet collector to periodically clean the collector.

An advantage of the present method, compared to other factory-made exhaust gas cleaning systems on the market, is that the entire operation will be carried out while the ships are underway or while in port, while the ship remains in operation, without needing the ship to go to a shipyard for tanking. Taking into account the above, all the work related to the preparation and installation of the system described in the present method, such as the process of the chimney conversion itself, is studied based on maintaining the normal operation of the ship. Therefore, while the main engine is not in operation, during the ship's stay in port, the existing chimney is converted into an exhaust gas desulphurization system.

The work to be carried out to convert the chimney to a flue gas desulphurisation system relates to the construction of manholes to allow access to the spray nozzle arrays, the construction of the spray nozzle system support points and the application of the anti-corrosion coating to the chimney surface. At the same time, the spray nozzle system has been designed in such a way that it can be installed through the openings of the chimney and without requiring special construction using scaffolding inside the chimney. The required piping for the intake and discharge of wash water, the locations and installation of pumps as well as peripheral equipment and necessary modifications can all be carried out while the ship is in operation. In addition, the nozzle arrays, their supports, and the supports for the access and maintenance platforms are designed to be removable.

In certain geographic locations and certain ports, flushing water discharge may not be permitted, so the arrangement described in the present invention may not work and the ship will resort to using low sulfur fuel. In this case, the desulfurization device is simply used as a flue gas exhaust, as before the modification, without the need for cooling, in the so-called dry mode. During dry operation, but also during the transition from dry to normal operation with flushing water, large thermal stresses develop on all surfaces of the modified chimney.

The conversion method is characterized by the fact that all the construction materials of the modified chimney are resistant to high temperatures. This is necessary so that the dry operation of the system can be carried out without restrictions as well as the transition from dry to normal operation with flushing water, during which large thermal stresses develop.

The method envisages the installation of peripheral elements characteristic of a Marine exhaust gas desulphurisation system, complying with Annex VI of the Marpol directive, including certified measurement of SOx / CO2 ratio, measurement of effluent pH, PAH, NTU, marine pumps of water, measuring temperature, pressure & water supply, which are controlled through the use of a logic controller, to control and record the process.

The present method is described below by way of example and with reference to the attached drawings, in which:

Initially, thermal spraying is applied to the internal surface of the existing chimney, so that it is coated with the appropriate alloy that will give it anti-corrosion protection. Then the individual equipment is installed:

Figure 1 shows a view of a ship's exhaust gas desulphurization system, arranged concentrically to the existing exhaust stack (Figure 1, [1]). The arrangement includes arrays (Figure 1, [2] ,[3] ,[4] ,[5] ,[6] ,[7]) of water spray nozzles (Figure 1, [26]) placed in the chimney (Figure 1, [1]), where the first array (Figure 1, [2]) as described in the section above has the function of cooling the exhaust gases and is positioned in the direction of the exhaust gas flow, the second array (Figure 1, [3] ) consists of nozzles with an acute-angle cone-type spray profile, which will smooth the exhaust gas flow, and the following arrays (Figure 1, [4], [5], [6], [7]) of nozzles alternate with spray nozzles of different sizes with a spray direction opposite to the exhaust gas flow. At the exhaust gas outlet in the upper part of the described exhaust gas cleaning system, a droplet collector (Figure 1, [8]) is installed as well as an array of nozzles (Figure 1, [9]) for washing said collector (Figure 1, [8]). Flushing water enters from a main water supply (Figure 1, [12]) and is distributed to the different arrays of nozzles, in which valves are placed (Figure 1, [13]), which regulate the water supply and isolate the system in case of dry operation. The wash water reacts with the exhaust gases and then ends up in a collection vessel (10) and from there to the drain line (Figure 1, [11]) of the wash water into the sea. Special manholes have also been constructed in the existing chimney (Figure 1, [14]) for the purpose of crew entry for system maintenance and inspection. Figure 1 also shows the top view of the chimney (Figure 1, [1]), which includes the supports for the nozzle arrays (Figure 1, [15]) and the supports for the access and maintenance platforms (Figure 1, [16 ]) that have been established within it. The nozzle assemblies (Figure 1, [15]), their supports and the supports for the access and maintenance platforms (Figure 1, [16]) are removable and their overall dimensions are suitable to be inserted through the opening of the existing chimney (Figure 1, [1]).

Figure 2 illustrates a variant of the system arranged eccentrically in the existing exhaust chimney (Figure 2, [1]).

Figures 3 and 4 show the system arranged at an angle to the existing flue (Figure 3, [1]) and (Figure 4, [1]).

Figure 5 illustrates the 3D model of the complete desulfurization system layout as it is installed in the existing engine room layout of the ship. It shows the main engine (Figure 5, [18]) of the ship as well as the electric engines (Figure 5, [19]) and their exhausts (Figure 5, [25]), the exhaust gases of which are led to the exhaust collection and diversion chamber (Figure 5, [17]).

Figure 6 illustrates the 3D model of a random array (Figure 6, [27]) of nozzles (Figure 6, [26]) spraying wash water. Each array of nozzles (Figure 6, [27]) is sized to fit into the existing flue (Figure 6, [1]) and each array is removable.

Figure 7 illustrates the arrangement of the modified chimney in its lower part where there are the specially designed inlet ports (Figure 7, [20]) and the flue gas collection and diversion chamber (Figure 7, [17]), as well as the re-entry ports ( Figure 7, [24]) in the ship's main chimney.

Claims (6)

Claims 1. Method of converting an existing ship chimney (Figure 1, [1]) into an exhaust gas desulphurization system, characterized by the following steps: a) use of thermal spraying of metal alloys inside the main engine chimney to create a corrosion protection coating, b) installation of rows of water spray nozzles (Figure 1, [2]-[7], [9]), c) creation of a chamber for collecting and diverting the exhaust gases of the main engine and electric engines (Figure 1, [17])., d) creation of a collection device (Figure 1, [10]) and disposal of the washing water (Figure 1, [11]). e) installation of a droplet collector (Figure 1, [8]) placed in the upper part of the device, which consists of corrugated plates. 2. Method, according to claim 1, characterized by the use of thermal spraying for corrosion protection from materials of construction resistant to high temperatures, to allow the use of the chimney when the desulfurization system is out of operation. 3. Method, according to claim 1, comprising the creation of an exhaust gas collection device of main and auxiliary engines, which consists of an exhaust gas collection and diversion chamber (Figure 1, [17]), placed eccentrically or concentrically with respect to the sprinkler axis of flushing water, cross-section at least equal to the sum of the cross-sections of the chimneys of the main engine and the auxiliary engines. In addition, the arrangement includes exhaust gas diversion ports (Figure 7, [20]) of an area at least equal to the cross-sectional area of the chimney of the main engine (Figure 5, [18]). Furthermore, the arrangement includes re-entry ports (Figure 7, [24]) of the exhaust gases, with an area at least equal to the sum of the cross-sectional areas of the chimneys of the main engine and the auxiliary engines. 4. A method according to claim 1, which provides for the installation of arrays of wash water spray nozzles (Figure 1, [26]) and (Figure 6, [26]) where each array may comprise a different size and type of nozzles, suitable for cooling, flow normalization and exhaust gas desulphurisation. 5. A method according to claims 1 and 4, which provides for the installation of arrays of wash water spray nozzles, of which: a) The first, lower array of spray nozzles (Figure 1, [2]), is characterized by nozzles with an obtuse angle cone type spray profile, producing small droplet sizes, with water sprayed in the direction of the exhaust gas flow, b) The second lower array (Figure 1, [3]), will have the function of smoothing the exhaust gas flow and is characterized by nozzles (Figure 1, [26]) and (Figure 6, [26]) with an acute-angle cone-type spray profile with water spray against the direction of the exhaust gas flow, c) The following arrays of nozzles (Figure 1, [4], [5], [6], [7]) alternate with spray nozzles (Figure 1, [26]) and (Figure 6, [ 26]) of different sizes with a spray direction opposite to the exhaust gas flow. 6. Method, according to claim 1, comprising a device for collecting (Figure 7, [10]) and draining the washing water (Figure 7, [11]), which is characterized by a configuration of the existing chimney (Figure 7, [1 ]) of the main engine in a collection container with the addition of a metal bottom, carrying a drainage pipe (Figure 7, [11]) of the flushing water, placed inside the exhaust gas collection and diversion chamber (Figure 7, [17]), between the diversion ports (Figure 7, [20]) and re-entry (Figure 7, [24]) of the exhaust gases.