FIELD

The present disclosure relates to evaluation of heat transfer at an evaporator channel such as an evaporator tube . In particular, the disclosure relates to evaluation of latent heat transferred to the evaporating medium at the evaporator channel . The disclosure is applicable to industrial systems , such as metallurgical furnaces .

BACKGROUND

Evaporator channels such as evaporator tubes are used in various applications throughout industry . Often, however, the heat transferred to the evaporator channel cannot be evaluated from process parameters outside the channels .

OBJECTIVE

An obj ective is to alleviate the disadvantages mentioned above .

In particular, it is an obj ective to facilitate evaluation of latent heat transferred to an evaporating medium at an evaporator channel .

SUMMARY

According to a first aspect , an arrangement for facilitating evaluation of heat transfer to an evaporating medium at an evaporator channel is disclosed . The arrangement comprises a first sensor configured for measuring volume flow of the evaporating medium at an inlet region of the evaporator channel , a second sensor configured for measuring temperature of the evaporating medium at the inlet region of the evaporator channel , a third sensor configured for measuring pressure of the evaporating medium at the inlet region of the evaporator channel , and a fourth sensor configured for measuring pressure of the evaporating medium at an outlet region of the evaporator channel .

This arrangement allows evaluation of heat transferred to the evaporating medium, which is in single-phase , liquid state at the inlet region of the evaporator channel . In particular, it facilitates evaluation of sensible and/or latent heat transferred to the evaporating medium . With the indicated measurement configuration, this can be straightforwardly done from response curves for pressure drop with respect to flow at a given temperature and a given pressure , both of which may be measured at the inlet region . As the evaporation channel becomes part of an industrial piece of equipment or is utili zed in an industrial process , the solution as disclosed can have maj or importance for evaluating process performance and its efficiency . With knowledge of the heat transfer, the process can be optimi zed or problems with the process equipment can be detected at an early stage .

In an embodiment , the arrangement comprises a fifth sensor configured for measuring temperature of the evaporating medium at an outlet region of the evaporator channel . This allows accounting for singlephase flows for the evaporating medium .

In an embodiment , the arrangement comprises a sensor configured for measuring temperature outside the evaporator channel within a region from which heat is transferred to the evaporating medium . This allows improving the evaluation of heat transfer and the evaluation of the overall heat transmission coefficient .

In an embodiment , the arrangement comprises a flow resistance configured for positioning in the evaporator channel upstream to an evaporation region of the evaporator channel to stabil i ze the flow of the evaporating medium . This can markedly improve the evaluation of heat transfer as it can be used to guarantee that the flow of evaporating medium in the evaporating region is accurately depicted by response curves dominated by second order behavior . The evaporation region is the region where heat is introduced into the evaporator channel for evaporating the evaporating medium . The flow resistance may therefore condition the flow of evaporating medium before heat is introduced into the evaporating medium within the evaporator channel . In particular, the flow resistance may be configured for positioning downstream to the third sensor . In an embodiment , the flow resistance is integrated with the first sensor, for example as a flow resistance with a differential pressure measurement for flow measurement . The flow resistance can be configured to introduce a pressure drop to the evaporating medium . The f low resi stance may comprise one or more orifice noz zles , allowing for an effective and controllable way of providing the pressure drop . In a further embodiment , the flow resistance is configured so that said pressure drop is at least as large as the pressure drop for the evaporating medium between the third sensor and the fourth sensor resulting from evaporation at the evaporator tube under operation . This has been found to allow providing stable response under various conditions , particularly for an evaporator channel configured for use as a cooling coil for cooling of hot clean or dust-laden gases or in fluidi zed bed configuration . The corresponding pressure drops may be configured specifically to an application of the evaporator tube .

In an embodiment , the arrangement comprises a calculating unit configured to evaluate the sensible and/or latent heat transferred to the evaporating medium . This allows the arrangement to directly provide a value for the sensible and/or latent heat . For thi s purpose , the response curves may be utili zed as indicated above .

In an embodiment , the arrangement comprises a cooling and/or heating device , such as a boiler, a roaster, a smelter, a fluid bed cooler or a heat exchanger . The evaporator channel can thus form a part of the device . A particularly important application is the evaporator channel forming a cooling coil of the device .

In an embodiment , the arrangement comprises a controller configured to determine one or more values indicative of the heat transfer to the evaporating medium based, at least , on input from the first sensor, the second sensor, the third sensor and the fourth sensor . It can thus be configured to provide an indication if a threshold for maintenance is exceeded, in particular based on the one or more values . This allows preventive and/or reactive maintenance .

According to a second aspect , a method for facilitating evaluation of heat transfer to an evaporating medium at an evaporator channel is disclosed . The method comprises measuring volume flow of the evaporating medium at an inlet region of the evaporator channel , measuring temperature of the evaporating medium at the inlet region of the evaporator channel , measuring pressure of the evaporating medium at the inlet region of the evaporator channel , and measuring pressure of the evaporating medium at an outlet region of the evaporator channel .

Instead of an "arrangement" , the arrangement disclosed may be reali zed as an "apparatus" . It is to be understood that the aspects and embodiments described above may be used in any combination with each other . Several of the aspects and embodiments may be combined together to form a further embodiment of the invention . Correspondingly, the method may comprise measuring temperature of the evaporating medium at an outlet region of the evaporator channel and/or measuring temperature outside the evaporator channel within a region from which heat is trans ferred to the evaporating medium . It may also comprise , for example by utili zing a calculating unit , evaluating the sensible and/or latent heat transferred to the evaporating medium .

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings , which are included to provide a further understanding and constitute a part of this specification, illustrate examples and together with the description help to explain the principles of the disclosure . In the drawings :

Fig . 1 illustrates an example of a device in a top-down view,

Fig . 2 illustrates an example of an evaporator channel element in a side view,

Fig . 3 schematically illustrates an example of an arrangement ,

Fig . 4 illustrates evaluation of heat transfer according to an example , and

Fig . 5 illustrates a process according to an example .

Like references are used to designate equivalent or at least functionally equivalent parts in the accompanying drawings .

DETAILED DESCRIPTION

The detailed description provided below in connection with the appended drawings i s intended as a description of examples and is not intended to represent the only forms in which the example may be constructed or util i zed . However, the same or equivalent functions and structures may be accomplished by different examples.

Figure 1 shows an example of a device 100 such as a cooling and/or heating device. In general, such a device may comprise one or more evaporator channels, and in the illustrated embodiment there are eight evaporator channel elements 110 in total (as numbered in the figure) , each of which actually involves a pair of evaporator channels 210, 220, as illustrated in Fig. 2. The device as illustrated, at least in part, in Fig. 1 may represent a cooling coil arrangement with eight double cooling coil elements in a top-down view as it is used in a fluidized bed furnace. In general, the device can be a boiler, a roaster, a smelter, a fluid bed cooler or a heat exchanger, or any device utilizing one or more cooling coils. For example, it may be a fluid bed device such as a fluid bed cooler or a heater, which may have multiple cooling coils. As an example, it can be a metallurgical device, e.g. a furnace, such as a metallurgical roasting furnace. The device can be configured for maintaining and/or limiting a process temperature by the evaporator channel (s) . The device may be configured for a fluid bed process and/or forced circulation, e.g. for a fluid bed process with a forced circulation boiler. In a device with multiple evaporator channels, the arrangement as described hereafter may be utilized for facilitating evaluation of heat transfer to an evaporating medium at any or all of the evaporator channels.

An evaporator channel in accordance with the present disclosure can be utilized at the device 100 as described above, for example as an integrated part thereof. The evaporator channel may be an evaporator tube. In particular, it may be a cooling coil, for example for a heating and/or a cooling device as described above. As known to a person skilled in the art , the evaporator channel is configured for a flow of an evaporating medium across the channel , e . g . within a tube , to transfer heat to the channel from its environment . The heat may be transferred to the evaporating medium to raise its temperature and/or cause it to be at least partially evaporated . The evaporating medium may comprise or consist of a subcooled or saturated liquid . As an example , the evaporating medium may comprise or consist of water, but other alternatives can also be feasible . The evaporator channel may be utili zed, for example , as part of a heat flux sensor and/or for evaluation of heat transfer and/or heat distribution inside a furnace .

The heat is transferred to the evaporator channel 110 from its environment at an evaporation region 130 , which is also indicated in Fig . 1 as an inside region of the device 100 , e . g . as an inside of a furnace . The evaporating medium is introduced into the evaporating channel through an inlet 112 of the evaporator channel and it escapes the evaporating channel through an outlet 114 of the evaporator channel , thereby defining a flow direction through the evaporator channel from the inlet to the outlet . The evaporator channel may be configured for the flow direction to be fixed or changeable , in which case the roles of the inlet and the outlet may be reversed . The evaporating medium may be provided as a liquid at the inlet . At the inlet , the evaporating medium may be in sub-cooled or saturated state . In particular, it may be in a single-phase state , such as a l iquid state . At the outlet , the evaporating medium may be in singlephase state , as liquid or steam in particular, or in a two-phase state , as liquid-vapor mixture in particular . Heat can thus be transferred to the evaporating medium in the evaporator channel in single-phase flow or in two-phase flow . Figure 2 shows an example of an evaporator channel element 200 (e . g . a double cooling coil arrangement ) , which may comprise one or more evaporator channels . The evaporator channel element can be utili zed at the device as described above . In the illustrated example , the element comprises an upper evaporator channel 210 and a lower evaporator channel 220 . Each evaporator channel comprises an inlet 112 for introducing evaporating medium into the corresponding evaporator channel and an outlet 114 through which the evaporating medium escapes from the evaporator channel .

Figure 3 shows an example of an arrangement 300 . The arrangement may be provided as a separate measuring arrangement , which may be configured for retrofitting to an existing device , for example as described above , or it may comprise the device 100 as described above and therefore be provided also as a greenfield installation .

The arrangement can be configured for evaluation or facilitating evaluation of heat transfer to an evaporating medium at an evaporator channel 110 as described above . The arrangement comprises a first sensor 310 configured for measuring volume flow of the evaporating medium at an inlet region of the evaporator channel , a second sensor 312 configured for measuring temperature of the evaporating medium at the inlet region of the evaporator channel , a third sensor 314 configured for measuring pressure of the evaporating medium at the inlet region of the evaporator channel , and a fourth sensor 320 configured for measuring pressure of the evaporating medium at an outlet region of the evaporator channel . The first sensor, the second sensor and the third sensor may be positioned in any order at the inlet region .

The arrangement may comprise a fifth sensor 322 configured for measuring temperature of the evapo- rating medium at an outlet region of the evaporator channel . It may also comprise one or more sensors 324 configured for measuring temperature outside the evaporator channel within a region from which heat is transferred to the evaporating medium .

The inlet region may correspond to the inlet 112 of the evaporator channel or a region in the vicinity of the inlet , from which the corresponding parameter value for the evaporating medium entering the evaporator channel can be measured before it is evaporated at the evaporator channel . Similarly, the outlet region may correspond to the outlet 114 of the evaporator channel or a region in the vicinity of the outlet , from which the corresponding parameter value for the evaporating medium escaping from the evaporator channel can be measured after it is evaporated at the evaporator channel . Heat is transferred 330 to the evaporating medium from outside the evaporator channel in the evaporation region 130 of the evaporator channel , which is between the inlet region and the outlet region .

For the purpose of simultaneous flow measurement and flow resistance , the first sensor 310 may be configured as flow resistance with a differential pressure measurement , for example orifice differential pressure measurement . In particular, the first sensor thus configured may thereby itself facilitate stabili zing the flow of the evaporating medium . The stabili zation may be done to avoid a flow instability, for example for a specified application range , and to ensure the applicability of the heat transfer evaluation . However, the arrangement may also comprise a separate flow resistance 340 to stabili ze the flow of the evaporating medium, as j ust described, within the evaporator channel , where the flow resistance may stabili ze the flow both upstream and downstream of its location . For this purpose , the f low resistance may be positioned in the evaporator channel upstream to the evaporation region . In particular it may be positioned downstream to the third sensor 314 , or to all of the first 310 , second 312 and third sensor 314 . The flow resistance can be configured to introduce a pressure drop to the evaporating medium for flow stabili zation . For thi s purpose , the flow resistance may comprise one or more flow resisting elements that may be separate from each other . Also for the flow stabili zation, the flow resistance may be integrated with the first sensor . It may thus consist of one or more flow resisting elements integrated with the first sensor and/or one or more flow resisting elements separate from the first sensor . In particular, the flow resistance may be configured for providing a pressure drop that is at least as large as the pressure drop for the evaporating medium between the third sensor and the fourth sensor resulting from evaporation at the evaporator tube under operation . The flow resistance may comprise or consist of one or more orifice noz zles or it may consist of other flow resistance equipment . The flow resistance may be specifically configured for the design of the evaporator channel .

The arrangement may comprise a calculating unit (not illustrated) configured to evaluate the sensible and/or latent heat transferred to the evaporating medium . It may be directly or indirectly coupled to all of the abovementioned sensors , for example by one or more wired and/or wireless connections . It may comprise one or more processors and one or more memories . It may also comprise program code , stored on the one or more memories , that causes , when executed by the processor ( s ) , to evaluate heat transfer to the evaporating medium . This can be done based on input from the aforementioned sensors .

Figure 4 illustrates an example for evaluation of heat transfer . It shows how, at a given tern- perature 410 of the evaporating medium ( as measurable by the second sensor 312 ) and pressure 415 of the evaporating medium ( as measurable by the third sensor 314 ) , the response curves 450 for the pressure drop 420 ( as measurable by the third 314 and the fourth sensor 320 ) as a function of the flow 430 of the evaporating medium is dependent on the heat transferred 440 to the evaporating medium . As this belongs to the domain of a person s kil led in the art , the heat transfer can be straightforwardly evaluated with the arrangement as disclosed . The flow of the evaporating medium may be represented by the mass flow, as has been illustrated in the figure , which may be straightforwardly obtained from the volume flow of the evaporating medium ( as measurable by the first sensor 310 ) . The pressure drop can be straightforwardly obtained as the pressure difference between the third sensor and the fourth sensor . The example of Fig . 4 is provided with water as the evaporating medium so that two-phase flow corresponds to mixture of liquid water and steam but corresponding response curves can be provided for other evaporating media as well .

Figure 5 shows an example of a process for facilitating evaluation of heat transfer to an evaporating medium at an evaporator channel . The process as a whole or any combination of its parts can be implemented as a method . The parts may be performed independently from each other and/or in any logical order .

A set of measurements is made . Pressure of the evaporating medium is measured 510 at the inlet region of the evaporator channel , for example by the third sensor as described above . Temperature of the evaporating medium is measured 510 at the inlet region of the evaporator channel , for example by the second sensor as described above . Enthalpy and/or density of the evaporating medium can be straightforwardly derived 512 from the pressure and the temperature at the inlet , as measured, for example by calculation or from a look-up table . Volume flow of the evaporating medium is measured 520 at an inlet region of the evaporator channel , for example by the first sensor as described above . Mass flow of the evaporating medium can be straightforwardly derived 522 from the volume flow, as measured, based on the known density of the evaporating medium at the inlet region . Pressure of the evaporating medium is measured 530 at an outlet region of the evaporator channel , for example by the fourth sensor as described above . The pressure drop between the inlet region and the outlet region can be straightforwardly derived from the pressure at the inlet region and the pressure at the outlet region, as measured .

Any calculations can be made after corresponding measurement results are available , either concurrently or after the other measurements .

With the measurements available as described above , the heat transferred to the evaporating medium can be straightforwardly derived 540 , as described in reference to Figure 4 , for example in terms of heat flux and/or total heat . For this purpose , response curves , such as characteristic diagrams , can be used 542 . They can be stored as a template such as a neural network and/or a multi-dimensional look-up table . Alternatively, or additionally, an online calculation of required data points may be performed . This approach is applicable , in particular, when the evaporating medium is in two-phase flow ( at the outlet ) . As is evident to a person skilled in the art , the type of the flow ( single-phase vs . two-phase ) can be straightforwardly recogni zed from the response curves . This is evident also from Figure 4 , where the response curves collapse on each other only at the low end of energy transferred into the evaporating medium .

In case the evaporating medium is in singlephase flow ( at the outlet ) , the heat transferred thereto can be evaluated by uti li zing an additional measurement . Temperature of the evaporating medium may then be measured 550 at the outlet region of the evaporator channel , for example by the fifth sensor as described above . With the measurements of both temperature and pressure of the evaporating medium at both the inlet and the outlet region, it is then straightforward to derive the heat transferred to the evaporating medium also in the single-phase flow, for example in terms of heat flux and/or total heat .

The arrangement and the process may be calibrated 502 with cold flow by measuring one or more response curves and adapting model parameters such as the roughness of the evaporator channel . The calibration may be repeated if the setup of the evaporator channel ( s ) has changed or if the evaporator channel ( s ) have been corroded or replaced .

The arrangement and the process may be configured for various applications , such as a heat flux sensor and/or evaluation of heat transfer inside a furnace . They may also be configured for identification of fouling of evaporator channels and/or adaptive evaporator channel cleaning methods . They also allow optimi zation of heat transfer in thermal processes .

In an example application, one or more evaporator channels , or cooling coils , are part of a waste heat boiler as the device , which may be operated in the forced circulation mode . With the arrangement as disclosed, the heat transfer inside the bubbling bed of the device towards individual evaporator channels and the boiler water distribution can both be measured and possible deficiencies can be detected . For example , the boiler water supply to individual evaporator channels can be measured via orifice differential pressure measurements at the inlet of each channel . To operate the process at maximum performance and throughput , tube fouling or problems with the circula- tion or fluidi zing process can be detected with the arrangement as disclosed . Beside the heat (which may be indicated in the units of power, e . g . kW) and the heat flux (which may be indicated in the units of power per area, e . g . kW/m2 ) also the heat transfer coefficient (which may be indicated in the units of power per the product of area and temperature , e . g . W/ (m2 K) ) can be evaluated utili zing the arrangement or process as disclosed . To guarantee a reliable operation at maximum capacity with highest availability ( avoiding damages ) , the process conditions can be adj usted or maintenance measures to the device or the evaporator channel ( s ) can be applied .

The arrangement may comprise and/or be coupled to a controller that is configured to evaluate the heat transfer to the evaporating medium . The controller may also be configured to determine whether the heat transfer satisfies one or more criteria, for example whether it is above or below one or more threshold values . This allows , for example , detection of malfunction at the evaporator channel and/or the device utili zing it . In response to the determination, the controller may be configured to perform an alert , such as a visual and/or an audible alert , and/or perform one or more corrective operations to directly or indirectly alter the heat transfer . This allows , for example , preventive maintenance measures to be performed, for example during operational times and/or maintenance times of the arrangement or the device utili zing it .

The controller may be configured to determine one or more values indicative of the heat transfer to the evaporating medium based, at least , on input from the first sensor, the second sensor, the third sensor and the fourth sensor . It can be configured to provide , based on the one or more values , one or more indications if a threshold for maintenance is exceeded . The threshold may be a threshold for preventive and/or reactive maintenance . It may correspond to one or more predetermined threshold values , such as maximum or minimum values for heat transfer . Alternative or additionally, it may correspond to an indication of a threshold deviation, such as a maximum deviation, for example from one or more values indicative of heat transfer for one or more other evaporator channels . The indication may be provided as the alert , as indicated above . The controller may comprise one or more processors . It may also comprise one or more memories comprising computer program code . The one or more memories comprising computer program code may be configured to cause the controller to perform any or all of the abovementioned functions , for example to evaluate heat transfer to the evaporating medium at the evaporator channel . For this purpose , the controller may be indirectly or directly coupled to any or all of the first , second, third, fourth and fifth sensor . It may be configured to receive , indirectly or directly, measurement results from any or all of the sensors .

The different functions discus sed herein may be performed in a different order and/or concurrently with each other .

Any range or device value given herein may be extended or altered without losing the effect sought , unless indicated otherwise . Also any example may be combined with another example unless explicitly disallowed .

Although the subj ect matter has been described in language specific to structural features and/or acts , it is to be understood that the subj ect matter defined in the appended claims is not necessarily limited to the specific features or acts described above . Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims .

It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments . The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages . It will further be understood that reference to ' an ' item may refer to one or more of those items .

The term ' comprising ' is used herein to mean including the method, blocks or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements .

Numerical descriptors such as ' first ' , ' second' , and the like are used in thi s text simply as a way of differentiating between parts that otherwise have similar names . The numerical descriptors are not to be construed as indicating any particular order, such as an order of preference , manufacture , or occurrence in any particular structure .

Although the invention has been described in conj unction with a certain type of apparatus and/or method, it should be understood that the invention is not limited to any certain type of apparatus and/or method . While the present inventions have been described in connection with a number of examples , embodiments and implementations , the present inventions are not so limited, but rather cover various modifications , and equivalent arrangements , which fall within the purview of the claims . Although various examples have been described above with a certain degree of particularity, or with reference to one or more individual embodiments , those skilled in the art could make numerous alterations to the disclosed examples without departing from the scope of this specification .