Heavy oil emulsified fuel evaporator system

Abstract: In a heavy oil emulsified fuel evaporator system in which a heavy oil emulsified fuel (11a), after preheated at a preheater (13), is led into an evaporator (14) to be heated and then to a separator (15) for separation of its water content, and the water content, after separated, is used as a preheating source medium for the preheater (13), the preheater (13) is constructed of a first heat exchanger (41) using steam as the preheating source medium and having a level switch (44a) and a second heat exchanger (42) communicating with said first heat exchanger (41) via a flow control valve (44b) and using hot water as the preheating source medium so that the heavy oil emulsified fuel to be heated is flown to said first heat exchanger (42) from said second heat exchanger (41). With this structure an operation control of the system is facilitated so that a suspended state of light oil content in the preheating source medium and thus the discharge of light oil content together with water content can be avoided.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to an evaporator system for separation of water content in a heavy oil emulsified fuel by way of heating. Description of the Prior Art: As heavy oil is of a high consistency nature, in order to make its handling of transportation and storage easier, heavy oil fuel is added in advance with an appropriate amount of water and surface active agent so as to form what is called a heavy oil emulsified fuel. When this heavy oil emulsified fuel is to be burned in a combustion furnace of a boiler etc., it is desirable to remove water content from the heavy oil emulsified fuel for combustion efficiency. It is to be noted that the preheating source medium and EP 0 760 451 discloses a prior art evaporator system comprising a fuel preheater, an evaporator and a water separator. A prior art evaporator system for separation of water content in the heavy oil emulsified fuel is shown in Fig. 7 and description will be made thereon. In Fig. 7, numeral 11 designates a tank, in which an emulsified fuel 11a is stored. Numeral 12 designates a pump, numeral 13 designates a preheater, numeral 14 designates an evaporator, numeral 15 designates a separator, numeral 16 designates a heating steam supply equipment and numeral 17 designates a pump. In the evaporator system of Fig. 7 having such equipment and machinery, the emulsified fuel 11a, containing water, in the tank 11 is fed into the preheater 13 via the pump 12 and a piping 11b. A heat exchanger tube 13a is provided within the preheater 13 for flow of heating water or steam, after separated, as a preheating source medium which is described later, and the emulsified fuel 11a is filled surrounding the heat exchanger tube 13a. the emulsified fuel 11a may be flown either on inside or on outside of the heat exchanger tube 13a. The emulsified fuel 11a outside of the heat exchanger tube 13a is preheated to a certain temperature through heat exchange with the preheating source medium and is sent to the evaporator 14 via a piping 13b. Within the evaporator 14 provided are a plurality of generating tubes 14a, 14b, 14c, for flow of the preheated emulsified fuel 11a. On the other hand, the emulsified fuel 11a is heated by a heating source medium surrounding the generating tubes 14a, 14b, 14c, the heating source medium being a heating steam, for example, which is supplied from the heating steam supply equipment 16 via a piping 16a, and the heating source medium of which temperature has been lowered is discharged through a piping 16b. Thus, the emulsified fuel 11a within the generating tubes 14a, 14b, 14c is boiled to be evaporated and is then sent to the separator 15 via a piping 14d. The emulsified fuel 11a fed into the separator 15 is separated into water content (steam) and heavy oil fuel. The water content separated from the emulsified fuel 11a at the separator 15 is sent to the preheater 13 via a piping 15a in a state of heating water or steam to be used as a preheating source which flows in said heat exchanger tube 13a of the preheater 13 and, after its temperature has been lowered, is discharged out of the system via a piping 15b. It is to be noted that a surplus water remaining after the separated water has been taken for said preheating source is extracted outside of the system via a valve 15c and a piping 15d to be used for an atomizing steam etc. Also, the heavy oil fuel of which water content has been separated at the separator 15 is taken out of the system via a piping 15e and a pump 17 to be burned in a combustion system (a boiler, for example) having main equipments, such as a tank, a burner, etc. which are not shown in the figure. In order to make effective use of heat input amount of the heating source medium fed into the evaporator 14, a heat regeneration type is used in which the water content separated from the emulsified fuel at the separator 15 is introduced into the preheater 13 as the preheating source medium so that its heat source is made use of repeatedly, and a design of construction consisting of the preheater 13, the evaporator 14, etc. having such a heating area as is compact to the extent possible is employed. In the prior art evaporator system as described above, it is essential to operate it so as to obtain such a high efficiency water separation as brings on a maximum thermal efficiency, a best compact-sized design of equipment and machinery and an always constant predetermined value of water content in the heavy oil emulsified fuel which is obtained after separation. In the mentioned combustion system (boiler etc.) for burning the separated heavy oil fuel, however, amount of use of the heavy oil fuel used therein is not always constant but varies unavoidably corresponding to load change in the boiler etc. For example, if flow rate of the emulsified fuel is increased from a certain flow rate, because the system is of a closed loop, amount of the preheating source medium from the piping 15a does not increase rapidly resulting in lowering of outlet temperature of the preheater and change of the operation conditions. Thus, when the amount of the emulsified fuel (hereinafter called a "load") sent to the preheater 13 from the tank 11 changes, because the system employs a heat regeneration type, there occurs a delay in delivery and receipt of heat and temperature in each portion changes, which results in that the water content in the emulsified fuel obtained after separation does not become constant, and as one countermeasure therefor, there is given unavoidably a considerable allowance in the design of heating area in the heat exchanger portion of each component equipment and machinery. On the other hand, there is mixed a small amount of light oil content in the water content separated at the separator 15 and the preheating source medium in which this light oil content is mixed is used for heat exchange at the preheater 13. When this preheating source medium is discharged in a state of steam (gas) from the preheater 13, the light oil content mixed therein in a state of vapor is condensed soon together with the water content so that the oil content is suspended in the water. The oil content once suspended in the water being hardly separated or removed by a general oil content treatment equipment, draining thereof into rivers and the like becomes impermissible and there occurs an obstacle in the operation of the evaporator system. Further, if there occurs a pressure reduction action in the separator 15, the water content in the emulsified fuel which is heated to a high temperature at the evaporator 14 flashes (evaporizes) rapidly and gets out hardly of the surrounding high consistency heavy oil fuel resulting in a state of bubbles in which the emulsified fuel surrounds the steam gas. As the result, volume of the fuel increases rapidly to become full in the separator 15 or to cause an overflow in the water content separation and extraction pipings, separation performance of the water content is deteriorated rapidly and a large amount of the oil content is discharged out of the system. SUMMARY OF THE INVENTION: In view of the problems as mentioned above in the prior art heavy oil emulsified fuel evaporator system, it is an object of the present invention to provide a heavy oil emulsified fuel evaporator system in which a heavy oil emulsified fuel, after preheated at a preheater, is led into an evaporator to be heated and then to a separator for separation of its water content and the water content, after separated, is used as a preheating source medium for said preheater, wherein no light oil content is discharged together with the separated water content. In order to attain said object to discharge no light oil content together with water content, the present invention provides a heavy oil emulsified fuel evaporator system characterized in that a preheater for preheating the heavy oil emulsified fuel of which water content is to be separated is constructed of a first heat exchanger using steam as the preheating source medium and having a level switch and a second heat exchanger communicating with the first exchanger via the flow control valve and using hot water as the preheating source medium so that the heavy oil emulsified fuel to be preheated is flown to the first heat exchanger from the second heat exchanger. According to this evaporator system of the present invention, such a heat exchanger is employed that the preheating source medium is the steam and high temperature hot water in the first preheater and the high temperature hot water and low temperature hot water in the second preheater, thereby evaluation of heat transfer characteristics in the respective preheater becomes facilitated. Thus, by employing a heat exchanger mainly for steam and a heat exchanger mainly for hot water, individual design with a high accuracy becomes possible and a compact-sized structure and a reduced cost can be attained. Further, in the system of piping wherein the hot water level in the preheater is detected and controlled, such an operation control as causes a small volume of hot water to flow so that the flow velocity of the preheating source medium in the state of steam does not reach a critical velocity can be done easily. According to such an operation control, a suspended state of the light oil content in the preheating source medium can be avoided, a subsequent oil content removal by a usual oily water separating equipment can be done easily and drainage into rivers and the like becomes possible. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a diagrammatic view showing a construction of an evaporator system. Fig. 2 is a graph showing a relationship between temperature difference in evaporator inlet and outlet temperatures and water content in a heavy oil emulsified fuel after separation of its water content. Fig. 3 is a diagrammatic view showing a construction of an other evaporator system. Fig. 4 is a diagrammatic view showing a construction of an evaporator system according to the present invention. Fig. 5 is an explanatory view showing a construction of a separator to be used for an evaporator system. Fig. 6 is a cross sectional view taken along line A-A of Fig 5. Fig. 7 is a diagrammatic view showing a construction of a prior art evaporator system. DESCRIPTION OF THE PREFERRED EMBODIMENTS: Here below, description will be made concretely on a heavy oil emulsified fuel evaporator system according to the present invention as well as on an operation method thereof, based on the embodiment shown in Figs. 4. It is to be noted that, in the embodiments below, a part of same construction as that shown in Fig. 7 is given a same numeral for simplicity of explanation. Firstly, an operation method of an evaporator system will be described with reference to Fig. 1. In Fig. 1, numeral 21a, 21b, 21c and 21d, respectively, designates a flow control valve, numeral 22a and 22b, respectively, designates a temperature sensor and numeral 23a designates a pressure sensor. The flow control valve 21a is provided in a piping 15a for introducing a separated water content to a preheater 13 from a separator 15 and the flow control valve 21b is provided in a piping for introducing steam to the piping 15a from an auxiliary steam source which is not shown in the figure. Also, the flow control valve 21c is provided in a piping 15d and the flow control valve 21d in a piping 16a. On the other hand, the temperature sensor 22a is provided in a piping 13b either at outlet of the preheater 13 or at inlet of an evaporator 14 and the temperature sensor 22b is provided in a piping 14d. Also, the pressure sensor 23a is provided in a piping 15a. Other construction is substantially same as that of the evaporator system shown in Fig. 7. The flow control valve 21a, which controls flow rate of the water content (steam) as a preheating source medium which is separated at the separator 15 and is introduced into the preheater 13, is opened and closed by a signal from the temperature sensor 22a provided either at the outlet of the preheater 13 or at the inlet of the evaporator 14 so as to control the flow rate of the preheating source medium flowing into the preheater 13 to a constant level of outlet temperature of the preheater 13 or of inlet temperature of the evaporator 14. Further, the flow control valve 21d is opened and closed by a signal from the temperature sensor 22b provided at outlet of the evaporator 14 so as to control flow rate of a heating steam to a predetermined constant level of outlet temperature of the evaporator 14. On the other hand, the flow control valve 21b, receiving a signal from the pressure sensor 23a in the piping 15a through which the preheating source medium flows, regulates flow rate of the steam from the auxiliary steam source (not shown) so as to maintain a constant pressure in the piping 15a. Also, the flow control valve 21c controls flow rate to be extracted outside of the system of the separated steam as the preheating source medium generated at the separator 15 and flowing in the piping 15a so as to maintain a constant pressure in the piping 15a. As mentioned above, the outlet temperature of the preheater 13 (or the inlet temperature of the evaporator 14) is detected and the flow control valve 21a is opened and closed so as to maintain this temperature constant, thereby the flow rate of the preheating source medium at the inlet of the preheater 13 is controlled. Further, the pressure in the piping for supplying the preheating source medium is detected by the pressure sensor 23a and, based on the signal from the pressure sensor 23a, the flow control valves 21b and 21c are opened and closed so as to maintain the constant pressure. Thus, with the constant supply pressure of the preheating source medium and the constant inlet temperature of the evaporator 14, the operation control is facilitated. In the operation control state with the constant inlet temperature of the evaporator 14, the outlet temperature of the evaporator 14 is controlled to a predetermined temperature, thus as is clear from a temperature relationship shown in Fig. 2, such an operation control as controls the water content in the heavy oil fuel to a desired value is realized and a constant and stable operation of the entire system becomes possible as well. Furthermore, in case of load change, the flow rate of the emulsified fuel flowing into the preheater 13 is increased or decreased and the temperature, pressure and flow rate at each of the above-mentioned portions change corresponding thereto, but by employing the operation control method as mentioned above, a rapid change in the inlet temperature and outlet temperature of the evaporator 14 and the pressure of the preheating source medium in the piping 15a is avoided so as to be suppressed into a slow change. As the result, change in the water content remaining in the heavy oil fuel after separated of its water content is avoided, and even in the case of load change, the operation to control the water content to a substantially constant and stable level becomes possible in the entire evaporator system as well. Next, a second operation method of an evaporator system will be described with reference to Fig. 3. In Fig. 3, numeral 31 designates a buffer tank, which is provided in a middle of a piping 13b for leading an emulsified fuel to an evaporator 14 from a preheater 13. Alternatively, in place of the buffer tank 31, a preheater of such a structure that a volume outside of a heat exchanger tube 13a (a portion where the emulsified fuel flows) in the preheater 13 is an increasable amount, which term "increasable amount" is defined to mean an amount of the emulsified fuel equivalent to one hour or more supplied into the evaporator 14 within a time range while there occur load changes. Other construction than the above is substantially same as that of the evaporator system shown in Fig. 1 and Fig. 7. In such emulsified fuel evaporator system shown in Fig. 3, the emulsified fuel of the increasable amount which has been preheated controlled to a predetermined temperature can be stored in advance in the buffer tank 31 or in the preheater 13. In case of load change, for example load increase, in a combustion system (boiler and the like) for burning the separated heavy oil, rotation of a pump 12 is increased to increase supply amount of the emulsified fuel into the preheater 13, that is, flow rate of the emulsified fuel to be introduced into the emulsified fuel evaporator system, and because the emulsified fuel of predetermined temperature is stored in advance in the increasable amount, the temperature of the emulsified fuel flowing into inlet of the evaporator 14 is maintained constant always within the range of time of the load change. Thus, simply by controlling the flow rate of heating steam as heating source medium to be supplied into the evaporator 14 so as to maintain outlet temperature of the evaporator 14 to a predetermined level, such an operation as is able to supply the heavy oil fuel having a predetermined amount of water content after separation of its water content, that is, the heavy oil fuel having a predetermined amount of water content irrespective of increase or decrease in the flow rate of the heavy oil fuel to be supplied into the combustion system, can be attained easily along the relationship shown in Fig. 2. In the evaporator system of the second embodiment as mentioned above, the emulsified fuel of predetermined temperature in the increasable amount is stored in advance in the buffer tank 31 or in the preheater 13, hence even in such an operation as cannot avoid a load change operation or in such an operation state within a time range while supply amount of the emulsified fuel to the preheater 13 increases or decreases, inlet temperature of the evaporator 14 is maintained constant always and by controlling outlet temperature of the evaporator 14 to a predetermined temperature, the water content in the heavy oil fuel after separation of its water content can be controlled to a predetermined value easily. Next, an emulsified fuel evaporator system according to the present invention will be described with reference to Fig. 4. In this evaporator system of the third embodiment, preheaters 41 and 42 in two-stages or more are provided in place of the preheater 13 in Fig. 1. It is to be noted that the preheaters 41 and 42 may be of a single unit of preheaters or a parallel arrangement of plural pieces. Also, a level switch 44a and a control valve 44b of a preheating source medium are provided to the preheater 41. The preheaters 41 and 42 have such heating area and structure that provide following functions in terms of heating characteristics. That is, an operation is controlled such that water level of the preheating source medium in the preheater 41 is controlled by the control valve 44b opened and closed by a signal from the level switch 44a so that the preheating source medium of steam state may not be introduced into the next preheater 42 from the preheater 41. As the result, a separated steam from the preheating source medium separated at a separator 15 and sent to the preheater enters first a heat exchanger tube 41a in the preheater 41 to change to a hot water state from the steam (gas) state through heat exchange with the surrounding emulsified fuel and is then introduced into a heat exchanger tube 42a of the next preheater 42 likewise to preheat the emulsified fuel and is discharged out of the system via a piping 15b. In the separated steam as the preheating source medium separated at the separator 15, there is mixed a light oil content and if such a case has occurred that flow velocity in the piping has become several tens m/s or more or has reached a critical velocity, the light oil content is suspended in the hot water to be discharged outside of the system from the preheater so that it is hardly removed of the drainage by a usual oily water separating equipment and drainage into rivers and the like becomes impermissible. On the other hand, if a single preheater is used, heat utilization must be done such that the preheating source medium changes to a low temperature hot water state from a high temperature steam state in that single preheater, but because exchange heat amount changes in proportion to amount of the emulsified fuel flowing in the preheater, position of a transition region between steam state and hot water state of the preheating source medium varies. As heat transfer characteristics between steam and hot water are different largely from each other, if steam or hot water is unknown of the preheating source medium in the preheater, an accurate design of the heating area will be difficult resulting unavoidably in a design with a large allowance, which brings on an enlarged structure and an increased cost. On the contrary, in the present third embodiment, such a heat exchanger is employed that the preheating source medium is the steam and high temperature hot water in the preheater 41 and the high temperature hot water and low temperature hot water in the preheater 42, thereby evaluation of heat transfer characteristics in the respective preheater becomes facilitated. Thus, by employing a heat exchanger mainly for steam and a heat exchanger mainly for hot water, individual design with a high accuracy becomes possible and a compact-sized structure and a reduced cost can be attained. Further, in the system of piping wherein the hot water level in the preheater is detected and controlled, such an operation control as causes a small volume of hot water to flow so that the flow velocity of the preheating source medium in the state of steam is not 10 m/s or more or does not reach a critical velocity can be done easily. That is, an operation control is done so that the flow velocity in the piping becomes several tens m/s or less, a suspended state of the light oil content in the preheating source medium can be avoided, a subsequent oil content removal by a usual oily water separating equipment can be done easily and drainage into rivers and the like becomes possible. An other operation method of an evaporator sytem shown in Figs. 5 and 6 will be described. Figs. 5 and 6 show only a separator 15 to be used in an evaporator system. The separator 15 shown in Fig. 5 has a structure wherein there are provided at opening portions on a side face thereof a transmitter 51 and receivers 52a, 52b and 52c. Said transmitter 51 and receiver 52a, 52b and 52c may be provided also in a plurality of sets thereof. If there occurs a pressure reduction action in the separator 15, water content in the emulsified fuel heated to a high temperature at an evaporator flashes (vaporizes) rapidly and gets out hardly of a surrounding high consistency heavy oil fuel resulting in a state of bubbles in which the heavy oil fuel surrounds the steam of gas. Sound wave is transmitted from the transmitter 51 at the opening portion on a side of vessel and is received by the receivers 52a, 52b and 52c provided upward and downward at the opening portions in the opposing wall. When the sound wave passes in the separator 15, there are differences in the velocity passing through the air and the heavy oil fuel and steam in the emulsified fuel and these differences in the receiving time of sound wave are measured and processed by a measuring device and computing device (not shown). In a normal operation state, the emulsified fuel is separated completely into the water content (steam) and the heavy oil fuel at the separator 15 and there is substantially only the steam in the range where the sound wave is projected from the transmitter 51 resulting in a constant receiving time. On the contrary, if there occur said bubbles, the heavy oil fuel increases in place of the steam resulting in variations in the receiving time of sound wave. Thus, a continuous prior detection of bubble generation phenomena in an abnormal operation becomes possible and discharge of the heavy oil fuel out of the system due to overflow can be prevented. Further, by a spreading energy of the sound wave, defoaming effect can be expected as well. As described above, according to an operation method of the heavy oil emulsified fuel evaporator system, outlet temperature of the preheater or inlet temperature of the evaporator is controlled constant, pressure in the preheating source medium supply piping for leading the preheating source medium into the preheater is controlled constant and temperature difference between the inlet temperature and the outlet temperature of the evaporator is controlled constant, thereby even in a case of load change, variations in the water content in the heavy oil fuel after separation of water content can be avoided. Also, in said operation method, a construction for storing the preheated emulsified fuel of the increasable amount in the preheater or between the preheater and the evaporator is employed, thereby even in a case of load change, the emulsified fuel of predetermined temperature can be supplied into the inlet of the evaporator and the water content in the heavy oil fuel can be maintained to a predetermined value easily. Further, the present invention provides a heavy oil emulsified fuel evaporator system in which the preheater for preheating the heavy oil emulsified fuel of which water content is to be separated is constructed of a first heat exchanger using steam as the preheating source medium and having a level switch and a second heat exchanger communicating with the first exchanger via the flow control valve and using hot water as the preheating source medium so that the heavy oil emulsified fuel to be preheated is flown to the first heat exchanger from the second heat exchanger. In said evaporator system, the heat exchanger, which is the preheater, is divided into the first heat exchanger using steam and hot water as the preheating source medium and the second heat exchanger using hot water only as the preheating source medium, hence evaluation of the heat transfer characteristics becomes easy and design of a high accuracy becomes possible. Further, hot water level in the preheater is controlled, thereby light oil content in the preheating source medium is prevented from becoming a suspended state. Also, an evaporator system might employ a separator having a transmitter for transmitting a sound wave and a receiver for receiving the sound wave, thereby bubble generation phenomena in the separator can be detected in advance continuously, so that discharge of the heavy oil fuel out of the system due to overflow can be prevented. It is understood that the invention is not limited to the particular construction and arrangement herein illustrated and described but embraces such modified forms thereof as come within the scope of the following claim.

Claims: A heavy oil emulsified fuel evaporator system in which a heavy oil emulsified fuel (11a), after preheated at a preheater (13), is led into an evaporator (14) to be heated and then to a separator (15) for separation of its water content, and the water content, after separated, is used as a preheating source medium for said preheater (13), characterized in that said preheater (13) is constructed of a first heat exchanger (41) using steam as the preheating source medium and having a level switch (44a) and a second heat exchanger (42) communicating with said first heat exchanger (41) via a flow control valve (44b) and using hot water as the preheating source medium so that the heavy oil emulsified fuel to be heated is flown to said first heat exchanger (42) from said second heat exchanger (41).

Inventors: HINO HIROKAZU, ICHINOSE TOSHIMITSU, TOKUDA KIMISHIRO, UEDA KATSUYUKI, HINO, HIROKAZU, ICHINOSE, TOSHIMITSU, TOKUDA, KIMISHIRO, UEDA, KATSUYUKI, HINO, HIROKAZU, MITSUBISHI HEAVY INDUSTRIES LTD, ICHINOSE, TOSHIMITSU, MITSUBISHI HEAVY IND. LTD., TOKUDA, KIMISHIRO, MITSUBISHI HEAVY INDUSTRIES LTD, UEDA, KATSUYUKI, MITSUBISHI HEAVY INDUSTRIES LTD.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1998
Main classification: F23K5
IPC codes: F23K5