Patent Description:
Boilers are well-known and used in many different heat exchange applications. For example, a boiler may be arranged after an exhaust gas source in the form of an engine to recover heat from exhaust gas produced by the engine. Such a boiler is often referred to as a heat recovery boiler. In such a boiler, a medium, typically water, conveyed through the boiler is heated by means of heat from the engine exhaust gas conveyed through the boiler. The engine may typically be operated at different loads, and the boiler is normally dimensioned for operation at any engine load, including operation at full, i.e. <NUM>%, engine load. One dimensioning criterion for the boiler may be the boiler exhaust gas pressure drop, and the boiler may be so dimensioned that the boiler exhaust gas pressure drop never exceeds 150mmWC. Typically, the higher the engine load is, the higher the boiler exhaust gas pressure drop is. Thus, the boiler exhaust gas pressure drop is typically the highest at full engine load. However, in reality, the engine is typically not run at full load but rather at <NUM>-<NUM>% of the full load which results in a boiler exhaust gas pressure drop considerably lower than 150mmWC. Consequently, the boiler will be over-dimensioned in most cases which makes the boiler unnecessarily expensive and bulky. Further, in many applications, steam will be produced during operation of the boiler, which steam can be used for different purposes if needed. However, if more steam than needed is produced, which typically could be the case during full engine load, steam has to be dumped. Therefore, the boiler is typically connected to equipment for dumping steam. Also this equipment is normally dimensioned for operation at any engine load and therefore over-dimensioned in most cases, and thus unnecessarily expensive and bulky.

<CIT> discloses a water tube boiler comprising water tube spirals. The space inside the innermost tube spiral is used as an exhaust gas by-pass channel in the boiler. The exhaust gas flow through the by-pass channel is controlled by means of a regulating means.

<CIT> discloses an exhaust apparatus of an internal combustion engine having two flow passages forming an exhaust flow passage connected to the internal combustion engine. The exhaust apparatus further comprises a valve member for controlling the exhaust flow through the flow passages.

<CIT> discloses an exhaust heat recovery system comprising an exhaust heat recovery unit disposed in an engine exhaust pipe, upstream and downstream flow paths for circulating a coolant between the exhaust heat recovery unit and the engine, a bypass flow path that communicates the upstream flow path to the downstream flow path to bypass the engine, and a valve arranged to adjust the flow in the bypass flow path.

An object of the present invention is to provide a boiler and a method of operating a boiler that at least partly solves the problems above. The basic concept of the invention is to dimension the medium and exhaust gas conveying means of the boiler, not for full exhaust gas source load, but rather for a typical exhaust gas source load, known as design load, and to provide the boiler with dedicated means for taking care of excess exhaust gas resulting from operation above the typical exhaust gas source load. The boiler and the method for achieving the object above is defined in the appended claims and discussed below.

A boiler according to the invention is arranged for transferring heat from exhaust gas or flue gas to a medium. The boiler comprises an exhaust gas inlet for receiving exhaust gas from an external first exhaust gas source, a first exhaust gas outlet for discharging exhaust gas from the external first exhaust gas source, and means for conveying exhaust gas from the external first exhaust gas source from said exhaust gas inlet to said first exhaust gas outlet. The boiler further comprises a medium inlet for receiving the medium, a medium outlet for discharging the medium, and means for conveying the medium from said medium inlet to said medium outlet. The boiler further comprises a bypass pipe for conveying exhaust gas from the external first exhaust gas source, from said exhaust gas inlet to said first exhaust gas outlet. The bypass pipe is enclosed by a circumferential wall of the boiler. Further, the boiler comprises a bypass regulator arranged to block or unblock the bypass pipe to regulate an exhaust gas flow through the bypass pipe. The boiler is characterized in that it comprises first pressure sensor for measuring a first exhaust gas pressure upstream the bypass pipe. Also, the boiler comprises a control unit communicating with the first pressure sensor and the bypass regulator and arranged to control the bypass regulator in dependence on said first pressure.

The boiler can be arranged for land-based or marine applications. The boiler may be installed onboard a moving vessel, such as a ship.

The medium to be heated can be any suitable medium, for example water. The medium may, or may not, change phases, such as go from liquid to gaseous phase, partly or completely, on its way through the boiler. For example, the medium inlet may be arranged to receive the medium at least partly in liquid phase, e.g. in the form of water, while the medium outlet may be arranged to discharge the medium at least partly in gaseous phase, e.g. in the form of steam.

The external first exhaust gas source may be of any suitable type, such as a diesel engine or a turbine.

Herein, the expression "conveying from an inlet to an outlet" and similar means "conveying in a direction from an inlet to an outlet" and not necessarily all the way from the inlet and all the way to the outlet. Thus, said means for conveying exhaust gas, said means for conveying the medium and said bypass pipe may, but need not, extend all the way between the respective inlets and outlets.

Since the bypass pipe is enclosed by the circumferential wall of the boiler, it may be arranged internally within the boiler. Such an internal bypass pipe may enable a compact and cost efficient design of the boiler, as well as a relatively short exhaust gas path between said exhaust gas inlet to said first exhaust gas outlet of the boiler. In turn, this may enable a relatively low pressure drop for exhaust gas flowing through the boiler. Further, such an internal bypass may be associated with relatively low thermal stresses in the boiler, as will be further discussed below. Moreover, such an internal bypass may enable use of a mechanically simple, compact and economical bypass regulator.

The circumferential wall can have any suitable shape, such as the shape of a tube with circular, oval, polygonal, rectangular, etc. , cross-section. The circumferential wall may further have any suitable design, such as be solid or hollow, and/or have a uniform or non-uniform thickness. As an example, the circumferential wall may be a so-called panel wall comprising a number of parallel tubes connected by means of solid wall portions. A cooling medium may be fed through these tubes for cooling exhaust gas conveyed through the boiler.

The components of the boiler could be made of any suitable material, for example carbon steel, stainless steel or aluminum.

The bypass pipe may have any suitable design, such as be straight or curved and have a circular or oval or polygonal cross section.

As said above, the bypass regulator is arranged to block or unblock the bypass pipe. Herein, "block" means "completely close" while "unblock" means "completely or partly open".

As used herein, "upstream" means "before" while "downstream" means "after", with respect to an exhaust gas flow direction. Thus, the first pressure sensor is arranged somewhere between the external first exhaust gas source and the bypass pipe of the boiler.

As used herein, "communicating" and similar means "communicating directly or indirectly". The communication can be wired or wireless.

As said above the control unit is arranged to control the bypass regulator in dependence on said first pressure. The first pressure may, or may not, be the only variable used by the control unit to control the bypass regulator.

At loads up to the typical load of the external first exhaust gas source for which the boiler is dimensioned, exhaust gas from the external first exhaust gas source may be fed through the boiler by said means for conveying exhaust gas. At higher loads, excess exhaust gas from the external first exhaust gas source may be fed through the boiler via the bypass pipe. The first exhaust gas pressure measured between the external first exhaust gas source and the bypass pipe of the boiler is dependent on the load of the external first exhaust gas source. By controlling the bypass regulator in dependence on said first exhaust gas pressure, the exhaust gas flow through the bypass pipe may be optimized. Thus, the provision of the bypass pipe makes it possible to dimension the rest of the boiler, as well as any steam dumping equipment connected thereto, based on a typical, instead of a maximum, load of the external first exhaust gas source, which is cost and space efficient.

The boiler may be so constructed that said means for conveying exhaust gas from said exhaust gas inlet to said first exhaust gas outlet comprise a first bundle of tubes. Further, said means for conveying the medium from said medium inlet to said medium outlet may comprise said circumferential wall of the boiler enclosing said first bundle of tubes.

The tubes, the bypass pipe and the circumferential wall could be made of the same material to get essentially the same temperature during operation of the boiler, which may enable relatively low thermal stresses in the boiler.

The tubes may have any suitable design, such as be straight, curved or coil- or helix-shaped and have a circular or oval or polygonal cross section, and the tubes may be similar or different from each other. The tubes may be provided with surface-enlarging elements, such as spiral fins, plate fins, or fins of any other suitable design.

The number of tubes may be two or more and they may extend along, and possibly also parallel to, each other and/or the bypass pipe.

Each of the tubes may have an inner volume which is smaller than an inner volume of the bypass pipe.

According to this embodiment, exhaust gas is fed through the boiler in tubes surrounded by the medium to be heated which is enclosed by said circumferential wall of the boiler, and heat exchange between exhaust gas and the medium is taking place through walls of the tubes. Such a boiler may be referred to as a smoke tube boiler. In dimensioning such a smoke tube boiler for a typical instead of a full load of the external first exhaust gas source, the number of tubes may be reduced which could make the boiler less costly and less space demanding even with the bypass pipe present. A reduced number of tubes means an increased exhaust gas velocity through the tubes, which, in turn, results in an increased efficiency of the heat transfer between exhaust gas and the medium, and also decreased formation of deposits on the tube inside walls. Further, the tubes of such a smoke tube boiler may be efficiently cleaned when the external first exhaust gas source is run at high load by rapidly cutting-off the exhaust gas flow through the bypass pipe by means of the bypass regulator to increase the exhaust gas velocity through the tubes for a short while to "blow them out", before again allowing an exhaust gas flow through the bypass pipe. This can be done one time, or repeatedly to create an exhaust gas wave in the tubes.

Instead of being designed as a smoke tube boiler, the boiler may be so constructed that said means for conveying the medium from said medium inlet to said medium outlet comprise one or more tubes. Further, said means for conveying exhaust gas from said exhaust gas inlet to said first exhaust gas outlet may comprise said circumferential wall of the boiler enclosing said one or more tubes.

Also these one or more tubes may have any suitable design, such as be straight, curved or coil- or helix-shaped and have a circular or oval or polygonal cross section, be similar or different from each other, extend along, and possibly also parallel to, each other and/or the bypass pipe, and be provided with surface-enlarging elements of any suitable design.

According to this embodiment, the medium to be heated is fed through the boiler in tubes surrounded by exhaust gas from the external first exhaust gas source, which exhaust gas is enclosed by said circumferential wall of the boiler, and heat exchange between exhaust gas and the medium is taking place through walls of the tubes. If the medium is water, such a boiler may be referred to as a water tube boiler.

The boiler may further comprise a second pressure sensor for measuring a second exhaust gas pressure downstream the bypass pipe. Further, the control unit may further communicate with the second pressure sensor and be arranged to control the bypass regulator also in dependence on said second pressure. Different external factors may affect the first and second pressures. By controlling the bypass regulator in dependence on both the first and second pressures, such external factors may be "cancelled" and the bypass regulator may be controlled in dependence on the conditions in the boiler only.

The first and second pressures may, or may not, be the only variables used by the control unit to control the bypass regulator. As an example, the control unit may be arranged to control the bypass regulator in dependence on a difference between the first pressure and the second pressure.

The second pressure sensor may have different positions. For example, the second pressure sensor may be arranged upstream the first exhaust gas outlet of the boiler, i.e. between the fist exhaust gas outlet and the bypass pipe. Such a position facilitates the provision of the second pressure sensor as an integrated component of the boiler.

Also the first pressure sensor may have different positions. As an example, the first pressure sensor may be arranged downstream the exhaust gas inlet of the boiler, i.e. between exhaust gas inlet and bypass pipe. Such a position facilitates the provision of the first pressure sensor as an integrated component of the boiler. As another example, the first pressure sensor may be arranged upstream the exhaust gas inlet of the boiler for measuring the first exhaust gas pressure before the boiler, i.e. between the external first exhaust gas source and the exhaust gas inlet of the boiler. Such a position may enable a more accurate measurement of the first exhaust gas pressure and may render it possible to directly measure an engine back pressure.

The bypass pipe may comprise an exhaust gas inlet for receiving exhaust gas and an exhaust gas outlet for discharging exhaust gas. Further, the bypass regulator may be arranged to cover one of the exhaust gas inlet and the exhaust gas outlet of the bypass pipe to block the bypass pipe. Such a bypass regulator may block the bypass pipe from the outside, which could enable a mechanically straightforward, reliable and accessible construction of the bypass regulator.

While the bypass regulator could be arranged to cover one of the exhaust gas inlet and the exhaust gas outlet of the bypass pipe, the other one of the exhaust gas inlet and the exhaust gas outlet of the bypass pipe could be arranged to be constantly open. This may enable a relatively uncomplicated design of the boiler and still a satisfactory control of the exhaust gas flow through the bypass pipe.

According to one embodiment, the bypass regulator is arranged to cover the exhaust gas outlet of the bypass pipe to block the bypass pipe. This embodiment provides a relatively mild environment for the bypass regulator since the temperature is typically lower at the exhaust gas outlet than at the exhaust gas inlet of the bypass pipe. In an alternative embodiment, the bypass regulator could instead be arranged to cover the exhaust gas inlet of the bypass pipe to block the bypass pipe.

The bypass regulator can have any suitable design. As an example, the bypass regulator may comprise a butterfly damper which may enable a mechanically straightforward, reliable and accessible construction of the bypass regulator.

The boiler may further comprise a third pressure sensor for measuring a steam pressure of steam discharged from the medium outlet. Further, the control unit may further communicate with the third pressure sensor and be arranged to control the bypass regulator also in dependence on said steam pressure.

The first pressure and the steam pressure may, or may not, be the only variables used by the control unit to control the bypass regulator.

Steam generated by the boiler and discharged from the medium outlet may be used for different purposes if needed. The steam generated but not needed is hereinafter referred to as excess steam. The amount of steam generated can be regulated by regulating the exhaust gas flow through the bypass pipe. More particularly, by increasing the exhaust gas flow through the bypass pipe, the generation of steam may be decreased, and vice versa. The more excess steam that is generated, the higher said steam pressure is. By controlling the bypass regulator in dependence on said steam pressure, the generation of steam may be adapted to the actual need. Consequently, production of excessive steam may be limited which, in turn, makes it possible to scale down equipment for handling excessive steam, such as steam dumping equipment.

According to one embodiment, the boiler further comprises a connection, communicating with said medium outlet, for dumping of steam discharged from the medium outlet, and a steam flow meter arranged to measure the amount of steam to be dumped. Further, the control unit communicates with the steam flow meter and is arranged to control the bypass regulator also in dependence on said amount of steam.

The first pressure and the amount of steam measured by the steam flow meter may, or may not, be the only variables used by the control unit to control the bypass regulator.

According to this embodiment, instead of, or in addition to, measuring the steam pressure and use this to control the bypass regulator as described above, the amount of steam to be dumped is measured and used to control the bypass regulator.

The boiler may further comprise a second exhaust gas outlet for discharging exhaust gas from a second exhaust gas source, and a second bundle of tubes for conveying exhaust gas from the second exhaust gas source to said second exhaust gas outlet, said circumferential wall of the boiler enclosing said second bundle of tubes. Such a boiler may be referred to as a composite boiler.

Also the tubes of the second bundle could be two or more, extend along and possibly also parallel to each other and/or the bypass pipe, be made of any suitable material, have any suitable design, be similar or different from each other, and each have an inner volume which is smaller than an inner volume of the bypass pipe.

In such a composite boiler, exhaust gas from the second exhaust gas source is fed through the boiler in tubes surrounded by the medium and contributes to the heating of the medium. The second exhaust gas source may be of any suitable type, such as an oil and/or gas fired burner.

The inventive method of operating a boiler to transfer heat from exhaust gas to a medium, comprises the steps of conveying exhaust gas from an external first exhaust gas source from an exhaust gas inlet to a first exhaust gas outlet of the boiler, and conveying the medium from a medium inlet to a medium outlet of the boiler. The method is characterized in further comprising the steps of measuring a first exhaust gas pressure upstream a bypass pipe of the boiler, which bypass pipe is arranged to convey exhaust gas from the external first exhaust gas source from said exhaust gas inlet to said first exhaust gas outlet, and regulating, in dependence on said first exhaust gas pressure, an exhaust gas flow through the bypass pipe.

The method may further comprise the steps of measuring a second exhaust gas pressure downstream the bypass pipe, and regulating, also in dependence on said second pressure, the exhaust gas flow through the bypass pipe.

The method may further comprise the steps of measuring a steam pressure of steam discharged from the medium outlet, and regulating, also in dependence on said steam pressure, the exhaust gas flow through the bypass pipe.

The method may further comprise the step of measuring an amount of steam, discharged from the medium outlet, to be dumped, and regulating, also in dependence on said amount of steam, the exhaust gas flow through the bypass pipe.

The above discussed advantages of the different embodiments of the boiler according to the invention are naturally transferable to the different embodiments of the method according to the invention.

The invention will now be described in more detail with reference to the appended schematic drawings, in which.

In <FIG> and <FIG> a boiler <NUM> is illustrated. The boiler <NUM> is arranged onboard a ship (not illustrated) and connected to an external first exhaust gas source in the form of a diesel engine <NUM> of the ship by a duct <NUM>. Exhaust gas EG1 generated by the diesel engine <NUM> is fed through the duct <NUM> to the boiler <NUM> for exhaust gas heat recovery. The boiler <NUM> comprises a carbon steel container <NUM>, in turn comprising a lower chamber or header <NUM>, a housing <NUM> and an upper chamber or header <NUM> arranged in succession in a vertical direction. The lower chamber <NUM> and the housing <NUM> both have a circular cylindrical form and are integrally formed so as to have similar cross sections and be concentrically arranged. The upper chamber <NUM> have a partly circular cylindrical form and a smaller cross section than the lower chamber <NUM> and the housing <NUM>.

The boiler <NUM> further comprises a first bundle <NUM> of carbon steel tubes <NUM> and a carbon steel bypass pipe <NUM> extending inside the container <NUM> between a lower tube plate <NUM> and an upper tube plate <NUM> of carbon steel, which plates form lower and upper walls of the housing <NUM> separating the housing <NUM> from the lower and upper chambers <NUM> and <NUM>. The bypass pipe <NUM> is partly surrounded by the tubes <NUM>. The tubes <NUM> and the bypass pipe <NUM> are straight and extend parallel to each other and to a longitudinal center axis c of the housing <NUM>. The tubes <NUM> and the bypass pipe <NUM> all have a circular cross section, and an inner volume of the bypass pipe <NUM> is considerably larger than an inner volume of each of the tubes <NUM>. The tubes <NUM> and the bypass pipe <NUM> are arranged to convey exhaust gas EG1 through the container <NUM>, which exhaust gas EG1 is received by the boiler <NUM> through an exhaust gas inlet <NUM> extending into the lower chamber <NUM> and discharged by the boiler <NUM> through a first exhaust gas outlet <NUM> extending out of the upper chamber <NUM>. Exhaust gas EG1 is fed through the exhaust gas inlet <NUM>, into the lower chamber <NUM>, through the tubes <NUM>, and possibly also through the bypass pipe <NUM> as will be further discussed below, into the upper chamber <NUM> and through the first exhaust gas outlet <NUM>.

Further, the boiler <NUM> comprises a furnace <NUM> arranged inside the container <NUM> and a second bundle <NUM> of carbon steel tubes <NUM> (illustrated in <FIG> only) extending inside the housing <NUM> between the furnace <NUM> and the upper tube plate <NUM> of the boiler. The tubes <NUM> are straight and extend parallel to each other and to a longitudinal center axis c of the housing <NUM>. The tubes <NUM> all have a circular cross section, and the inner volume of the bypass pipe <NUM> is considerably larger than an inner volume of each of the tubes <NUM>. The tubes <NUM> are arranged to convey exhaust gas EG2 from a second exhaust gas source, in the form of an oil-fired burner (not illustrated) arranged inside the furnace <NUM>, through the housing <NUM> before the exhaust gas EG2 leaves the boiler <NUM> through a second exhaust gas outlet <NUM> arranged at the upper tube plate <NUM>.

During operation of the engine <NUM>, the boiler <NUM> and possible the oil-fired burner, the housing <NUM> is filled with a medium, here water, which is fed into the housing <NUM> through a medium inlet <NUM>. Further, exhaust gas EG1 is fed through the tubes <NUM> and possibly the bypass pipe <NUM>, and exhaust gas EG2 is fed through the tubes <NUM> if the oil-fired burner is running. The water surrounds and flows around the tubes <NUM>, the tubes <NUM> and the bypass pipe <NUM>, and since the water is colder than the exhaust gas EG1 and EG2, heat is transferred from the exhaust gas, through walls of the tubes and the furnace, to the water which is heated and leaves the boiler <NUM>, in the form of a mixture of water and steam, through a medium outlet <NUM>. Since a circumferential wall <NUM> of the housing <NUM>, the tubes <NUM>, the bypass pipe <NUM> and the tubes <NUM> are made of the same material and all immersed in a common water volume, their temperatures will differ relatively little, which will cause relatively limited thermal stress in the boiler. Thus, the first bundle <NUM> of tubes <NUM> and the bypass pipe <NUM> serves as means for conveying the exhaust gas EG1 from the exhaust gas inlet <NUM> to the first exhaust gas outlet <NUM>, while the circumferential wall <NUM> of the housing <NUM> serves as means for conveying the medium from the medium inlet <NUM> to the medium outlet <NUM>.

The diesel engine <NUM> operates optimally when the boiler exhaust gas pressure drop is 150mmWC or lower. The boiler <NUM> is so dimensioned that the boiler exhaust gas pressure drop pressure is approximately 150mmWC at a diesel engine design load which is <NUM>-<NUM>% of the maximum diesel engine load. When the engine is operated at the design load or lower, the exhaust gas EG1 will be conveyed through the housing <NUM> through the tubes <NUM>. However, if the diesel engine, for whatever reason, is operated at a load above the design load, the engine exhaust gas EG1 will be conveyed through the housing <NUM> also through the bypass pipe <NUM> to avoid an increase of the engine back pressure. The exhaust gas flow through the bypass pipe <NUM> is regulated by means of a bypass regulator in the form of a butterfly damper <NUM>. The butterfly damper <NUM> is arranged at an exhaust gas outlet <NUM> of the bypass pipe <NUM> to open it and allow passage of exhaust gas EG1, or close it and prevent passage of exhaust gas EG1. In <FIG> and <FIG> the butterfly damper <NUM> is illustrated closed. An exhaust gas inlet <NUM> of the bypass pipe <NUM> is constantly open.

The boiler <NUM> comprises a control unit <NUM> connected to the butterfly damper <NUM> to control the opening and closing of it. The control unit <NUM> communicates with a first pressure sensor <NUM> arranged in the lower chamber <NUM> of the boiler <NUM> to measure a first exhaust gas pressure therein, and a second pressure sensor <NUM> arranged in the upper chamber <NUM> of the boiler <NUM> to measure a second exhaust gas pressure therein. The difference between the second and first exhaust gas pressures is directly related to the engine back pressure, and the control unit <NUM> is arranged to control the opening and closing of the butterfly damper <NUM> in dependence on this pressure difference. Accordingly, if the pressure difference exceeds a pre-set limit value, then the butterfly damper <NUM> will be open to a degree dependent on the pressure difference. However, if the pressure difference is below the pre-set limit value, then the butterfly damper <NUM> will be closed.

As mentioned above, the boiler <NUM> produces steam which leaves the housing <NUM> through the medium outlet <NUM>. This steam can be used for different purposes onboard the ship. If the steam generated by the exhaust gas EG1 from the diesel engine <NUM> is not sufficient, the oil-fired burner in the furnace <NUM> can be operated for generation of additional steam by means of the exhaust gas EG2 from the burner. Naturally, in an alternative embodiment of the boiler, the furnace <NUM>, the second bundle <NUM> of tubes <NUM> and the second exhaust gas outlet <NUM> could be omitted.

Thus, by means of the bypass pipe <NUM>, the butterfly damper <NUM> and the control unit <NUM>, the boiler exhaust gas pressure drop can be maintained at 150mmWC or lower even when the engine load exceeds the design load. Further, the bypass pipe <NUM>, the butterfly damper <NUM> and the control unit <NUM> offer a possibility of effectively cleaning the boiler <NUM> by operating the engine <NUM> above the design load, and the boiler <NUM> with an exhaust gas flow through the bypass pipe <NUM>, before suddenly cutting off the exhaust gas flow through the bypass pipe <NUM> by means of the butterfly damper <NUM> to "blow out" deposits from inside the tubes <NUM>.

In <FIG> another boiler <NUM> is illustrated. The boiler <NUM> is very similar to the boiler <NUM> and hereinafter the distinguishing features of the boiler <NUM> will be focused on. The boiler <NUM> comprises the first pressure sensor <NUM> but lacks the second pressure sensor <NUM> of the boiler <NUM>. In the boiler <NUM>, the first pressure sensor <NUM> is positioned directly after the diesel engine <NUM> and arranged to measure the engine back pressure of the diesel engine <NUM>. The control unit <NUM> is arranged to control the opening and closing of the butterfly damper <NUM> in dependence on this engine back pressure.

In <FIG> another boiler <NUM> is illustrated. The boiler <NUM> is very similar to the boiler <NUM> and hereinafter the distinguishing features of the boiler <NUM> will be focused on. In accordance with the previous description, liquid water is transformed into steam inside the boiler <NUM> through heat exchange with the exhaust gas EG1 and possibly the exhaust gas EG2. This steam can be used for different purposes onboard the ship. The more exhaust gas EG1 that is generated by the engine <NUM>, the more steam may be produced by the boiler <NUM>. Further, the more of the generated exhaust gas EG1 that passes through the tubes <NUM>, the more steam is produced. In other words, for a specific engine load, most steam is produced if all the exhaust gas EG1 passes the housing <NUM> through the tubes <NUM>, and no exhaust gas EG1 passes through the bypass pipe <NUM>, since the exhaust gas flow velocity, and therefore the heat transfer efficiency, will be lower for the bypass pipe <NUM> than for the tubes <NUM>. If more steam than needed is produced by the boiler <NUM>, the excess steam is dumped by means of steam dumping equipment (not illustrated) connected to the boiler <NUM>. By means of the bypass pipe <NUM>, the production of excess steam can be limited, which means that the steam dumping equipment capacity can be reduced.

Besides the first and second pressure sensors <NUM> and <NUM>, the boiler <NUM> comprises a third pressure sensor in the form of a steam pressure sensor <NUM> arranged at a connection extending from the medium outlet <NUM> of the boiler <NUM>. The control unit <NUM> is arranged to communicate with the steam pressure sensor <NUM> and control the opening and closing of the butterfly damper <NUM> also in dependence on a steam pressure measured by means of the steam pressure sensor <NUM>. Accordingly, if the steam pressure exceeds a pre-set limit value, then the butterfly damper <NUM> will be open to a degree dependent on the size of the steam pressure. If the steam pressure is below the pre-set limit value, but the difference between the second and first exhaust gas pressures, measured by the first and second pressure sensors <NUM> and <NUM>, exceeds the pre-set limit value, then the butterfly damper <NUM> will be open to a degree dependent on the size of the pressure difference. If the steam pressure is below the pre-set limit value, and the pressure difference is below the pre-set limit value, then the butterfly damper <NUM> will be closed.

Thus, by means of the bypass pipe <NUM>, the butterfly damper <NUM> and the control unit <NUM>, the production of steam can be adapted to the actual need for steam such as to reduce the amount of steam that has to be dumped and thereby enable down-scaling of the steam dumping equipment connected to the boiler.

In <FIG> another boiler <NUM> is illustrated. The boiler <NUM> is very similar to the boiler <NUM> and hereinafter the distinguishing features of the boiler <NUM> will be focused on. The steam produced by the boiler <NUM> and output from the medium outlet <NUM> is either fed through a connection <NUM> for use onboard the ship or fed through a connection <NUM> to be dumped. The boiler <NUM> comprises a steam flow meter <NUM> instead of the steam pressure sensor <NUM> of the boiler <NUM>. The steam flow meter <NUM> is arranged at the connection <NUM> for measuring a flow of steam to be dumped. Instead of controlling the opening and closing of the butterfly damper <NUM> in dependence on the measured steam pressure, the control unit <NUM> of the boiler <NUM> is arranged to control the opening and closing of the butterfly damper <NUM> in dependence on the measured flow of steam in the connection <NUM>.

In <FIG> another boiler <NUM> is illustrated. The boiler <NUM> has some similarities to the boiler <NUM> and hereinafter the distinguishing features of the boiler <NUM> will be focused on. The boiler <NUM> is arranged onboard a ship (not illustrated) and connected to an external first exhaust gas source in the form of a diesel engine (not illustrated). Exhaust gas EG1 generated by the diesel engine is fed to the boiler <NUM> for exhaust gas heat recovery. The boiler <NUM> comprises a container <NUM>, in turn comprising a lower chamber <NUM>, a housing <NUM> and an upper chamber <NUM> arranged in succession in a vertical direction. The lower and upper chambers <NUM> and <NUM> and the housing <NUM> all have a circular cylindrical form and are integrally formed so as to have similar cross sections and be concentrically arranged.

The boiler <NUM> further comprises a third bundle <NUM> of tubes <NUM>, which extend between a lower tube plate <NUM> and an upper tube plate <NUM>, which plates form lower and upper walls of the housing <NUM> separating the housing <NUM> from the lower and upper chambers <NUM> and <NUM>, and a parallel bypass pipe <NUM> extending inside the housing <NUM>. The tubes <NUM> are arranged to convey water and steam through the housing <NUM>, water being received by the boiler <NUM> through a medium inlet <NUM> extending into the lower chamber <NUM>, and steam being discharged from the boiler <NUM> through a medium outlet <NUM> extending out of the upper chamber <NUM>. The housing <NUM> and the bypass pipe <NUM> are arranged to convey exhaust gas EG1 through the boiler <NUM>, which exhaust gas EG1 is received by the boiler <NUM> through an exhaust gas inlet <NUM> extending into a lower portion of the housing <NUM> and discharged from the boiler <NUM> through a (first) exhaust gas outlet <NUM> extending out of an upper portion of the housing <NUM>.

During operation of the engine and the boiler <NUM>, exhaust gas EG1 is fed through the housing <NUM>. A circumferential wall <NUM> of the housing <NUM> serves as means for conveying the exhaust gas EG1 from the exhaust gas inlet <NUM> to the (first) exhaust gas outlet <NUM>. Also, exhaust gas EG1 is possibly fed through the bypass pipe <NUM>, as will be further discussed below. Inside the housing <NUM> exhaust gas EG1 surrounds and flows around the tubes <NUM> and the bypass pipe <NUM>. Further, water is fed from the medium inlet <NUM> and into the tubes <NUM>, and since the water is colder than the exhaust gas EG1, heat is transferred from the exhaust gas EG1, through walls of the tubes <NUM>, to the water in the tubes <NUM> which is heated and leaves the boiler <NUM>, in the form of steam or a mix of water and steam, through the medium outlet <NUM>. Thus, the bundle <NUM> of tubes <NUM> serves as means for conveying the water and steam from the medium inlet <NUM> to the medium outlet <NUM>.

When the engine is operated at design load or lower, the exhaust gas EG1 will be conveyed through the housing <NUM> outside the bypass pipe <NUM>. However, if the engine is operated at a load above design load, the engine exhaust gas EG1 will be conveyed through the housing <NUM> also via the bypass pipe <NUM> to avoid a boiler exhaust gas pressure above 150mmWC. The exhaust gas flow through the bypass pipe <NUM> is regulated by means of a butterfly damper <NUM> arranged at an exhaust gas outlet <NUM> of the bypass pipe <NUM>. An exhaust gas inlet <NUM> of the bypass pipe <NUM> is constantly open.

The boiler <NUM> comprises a control unit <NUM> connected to the butterfly damper <NUM> to control opening and closing of it based on a pressure difference between a first exhaust gas pressure measured upstream the bypass pipe <NUM> by means of a first pressure sensor <NUM> and a second exhaust gas pressure measured downstream the bypass pipe <NUM> by means of a second pressure sensor <NUM>.

In <FIG> another boiler <NUM> is illustrated. The boiler <NUM> has similarities to the boiler <NUM> and hereinafter the distinguishing features of the boiler <NUM> will be focused on. The boiler <NUM> comprises a housing <NUM> defined by a cylindrical circumferential wall <NUM> and lower and upper walls <NUM> and <NUM>, respectively. The boiler <NUM> further comprises a number of helical tubes <NUM> (here two), which extend around a bypass pipe <NUM> inside the housing <NUM>. The tubes <NUM> are arranged to convey water and steam through the housing <NUM>, water being received by the boiler <NUM> through a medium inlet <NUM> extending into a lower portion of the housing <NUM>, and steam, or a mixture of steam and water, being discharged from the boiler <NUM> through a medium outlet <NUM> extending out of an upper portion of the housing <NUM>. The housing <NUM> and the bypass pipe <NUM> are arranged to convey exhaust gas EG1 from a diesel engine (not illustrated) through the boiler <NUM>, which exhaust gas EG1 is received by the boiler <NUM> through an exhaust gas inlet <NUM> extending through the lower wall <NUM> of the housing <NUM> and a (first) exhaust gas outlet <NUM> extending through the upper wall <NUM> of the housing <NUM>.

The boiler <NUM> comprises a butterfly damper <NUM> arranged at an exhaust gas outlet <NUM> of the bypass pipe <NUM> for regulating an exhaust gas flow through the bypass pipe <NUM>. An exhaust gas inlet <NUM> of the bypass pipe <NUM> is constantly open. Further, the boiler <NUM> comprises a control unit <NUM> connected to the butterfly damper <NUM> to control opening and closing of it based on a pressure difference between a first exhaust gas pressure measured upstream the bypass pipe <NUM> by means of a first pressure sensor <NUM> and a second exhaust gas pressure measured downstream the bypass pipe <NUM> by means of a second pressure sensor <NUM>.

The above described embodiments of the present invention should only be seen as examples. A person skilled in the art realizes that the embodiments discussed can be varied and combined in a number of ways without deviating from the inventive conception.

As an example, the second pressure sensor could be omitted also in the boilers illustrated in <FIG>. Additionally/alternatively, the first pressure sensor could be arranged upstream the exhaust gas inlet of the boiler to measure the engine back pressure.

As another example, also the boilers illustrated in <FIG> and <FIG> could comprise a third pressure sensor for measuring a steam pressure of steam discharged from the medium outlet. Similarly, also the boilers illustrated in <FIG>, <FIG> and <FIG> could comprise a connection for steam dumping and a steam flow meter for measuring the amount of steam to be dumped.

The bypass regulator need not be designed as a butterfly damper but could be designed in any suitable way, for example as a gas damper, a single or multi blade damper, a louver damper, a guillotine damper or an inlet vane damper.

As an alternative to being arranged to block an end of the bypass pipe from the outside, the bypass regulator could instead be arranged inside the bypass pipe and/or be arranged to block the bypass pipe at an intermediate portion thereof.

Claim 1:
A boiler (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) for transferring heat from exhaust gas (EG1, EG2) to a medium, the boiler (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising an exhaust gas inlet (<NUM>, <NUM>, <NUM>) for receiving exhaust gas (EG1) from an external first exhaust gas source (<NUM>), a first exhaust gas outlet (<NUM>, <NUM>, <NUM>) for discharging exhaust gas (EG1) from the external first exhaust gas source (<NUM>), means (<NUM>, <NUM>, <NUM>, <NUM>) for conveying exhaust gas (EG1) from the external first exhaust gas source (<NUM>) from said exhaust gas inlet (<NUM>, <NUM>, <NUM>) to said first exhaust gas outlet (<NUM>, <NUM>, <NUM>), a medium inlet (<NUM>, <NUM>, <NUM>) for receiving the medium, a medium outlet (<NUM>, <NUM>, <NUM>) for discharging the medium, means (<NUM>, <NUM>, <NUM>) for conveying the medium from said medium inlet (<NUM>, <NUM>, <NUM>) to said medium outlet (<NUM>, <NUM>, <NUM>), a bypass pipe (<NUM>, <NUM>, <NUM>) for conveying exhaust gas (EG1) from the external first exhaust gas source (<NUM>) from said exhaust gas inlet (<NUM>, <NUM>, <NUM>) to said first exhaust gas outlet (<NUM>, <NUM>, <NUM>), which bypass pipe (<NUM>, <NUM>, <NUM>) is enclosed by a circumferential wall (<NUM>, <NUM>, <NUM>) of the boiler (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), and a bypass regulator (<NUM>, <NUM>, <NUM>) arranged to block or unblock the bypass pipe (<NUM>, <NUM>, <NUM>) to regulate an exhaust gas flow through the bypass pipe (<NUM>, <NUM>, <NUM>), characterized in further comprising a first pressure sensor (<NUM>, <NUM>, <NUM>) for measuring a first exhaust gas pressure upstream the bypass pipe (<NUM>, <NUM>, <NUM>), and a control unit (<NUM>, <NUM>, <NUM>) communicating with the first pressure sensor (<NUM>, <NUM>, <NUM>) and the bypass regulator (<NUM>, <NUM>, <NUM>) and arranged to control the bypass regulator (<NUM>, <NUM>, <NUM>) in dependence on said first pressure, and further comprising a second pressure sensor (<NUM>, <NUM>, <NUM>) for measuring a second exhaust gas pressure downstream the bypass pipe (<NUM>, <NUM>, <NUM>), the control unit (<NUM>, <NUM>, <NUM>) further communicating with the second pressure sensor (<NUM>, <NUM>, <NUM>) and being arranged to control the bypass regulator (<NUM>, <NUM>, <NUM>) also in dependence on said second pressure.