Heavy oil emulsified fuel evaporator system and operation method thereof

Abstract: Heavy oil emulsified fuel (11a) is preheated at a preheater (13), is heated at an evaporator (14) and is led into a separator (15) to be separated of its water content. Water content, after separated, is sent via a piping (15a) to be used as the preheating source medium for the preheater (13). Inlet temperature of the evaporator is controlled constant and pressure in the piping for leading the preheating source medium into the preheater is also controlled constant. Further, temperature difference of outlet temperature relative to the inlet temperature of the evaporator is controlled constant. Thereby, the water content in the heavy oil fuel coming out of the separator can be maintained to a predetermined value irrespective of load change in a heavy oil fuel combustion equipment and no light oil content is discharged together with the separated water content.

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 and an operation method thereof. 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. A prior art evaporator system for separation of water content in the heavy oil emulsified fuel is shown in Fig. 4 and description will be made thereon. A similar system is described in EP O 760 451 A2. In Fig. 4, 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. 4 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. It is to be noted that the preheating source medium and 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 an operation method of 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 water content separation to a predetermined level is enabled irrespective of load change in a heavy oil fuel combustion equipment. In order to attain said object to enable a predetermined water content separation constantly, the present invention provides an operation method of a heavy oil emulsified fuel evaporator system as defined in claim 1 and a heavy oil emulsified fuel evaporator system as defined in claim 3. In case of load change, flow rate of the emulsified fuel flowing into the preheater 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 above operation control method of the present invention, a rapid change in the inlet temperature and outlet temperature of the evaporator and the pressure of the preheating source medium in a piping 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. In the evaporator system to which said operation method is applied, it is desirable to employ a construction for storing the emulsified fuel of an increasable amount, as preheated, in the preheater or between the preheater and the evaporator. With this construction wherein the constant temperature emulsified fuel of the increasable amount it stored in advance, even in the case of load change, the emulsified fuel of a predetermined temperature can be supplied into the inlet of the evaporator and the water content in the heavy oil fuel separated thereby can be maintained to a predetermined value constantly. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a diagrammatic view showing a construction of an evaporator system according to a first embodiment of the present invention. 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 evaporator system according to a second embodiment of the present invention. Fig. 4 is a diagrammatic view showing a construction of a prior art evaporator system. DESCRIPTION OF THE PREFERRED EMBODIMENTS: Herebelow, 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 embodiments shown in Figs. 1 to 3. It is to be noted that, in the embodiments below, a part of same construction as that shown in Fig.4 is given a same numeral for simplicity of explanation. (First Embodiment) Firstly, an embodiment of operation method of an evaporator system according to the present invention 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. 4. 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. (Second Embodiment) Next, a second embodiment 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. 4. In such emulsified fuel evaporator system shown in Fig. 3, the emulsified fuel of the increasable amount which has been preheated controlledly 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.

Claims: A method of operating 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 the outlet temperature of said preheater (13) or the inlet temperature of said evaporator (14) is controlled to be constant, the pressure in a preheating source medium supply piping (15a) for leading said preheating source medium into said preheater (13) is controlled to be constant, and temperature difference of the outlet temperature relative to the inlet temperature of said evaporator (14) is controlled to be constant. A method of operating a heavy oil emulsified fuel evaporator system as claimed in claim 1, characterized in that the emulsified fuel of an increasable amount, as preheated, is stored in said preheater (13) or between said preheater (13) and said evaporator (14). A heavy oil emulsified fuel evaporator system comprising a preheater (13) for preheating a heavy oil emulsified fuel (11a), an evaporator (14) for heating said emulsified fuel (11a) after the same has been preheated in the preheater (13), and a separator (15) for separation of the water content of said emulsified fuel (11a) heated in the evaporator (14), wherein the water content, after separated, is used as a preheating source medium for said preheater (13), characterized in that a flow control valve (21a) is provided for controlling the flow rate of the separated water content as the preheating source medium from the separator (15) to the preheater (13), a flow control valve (21b) is provided for controlling the flow rate of steam from an auxiliary steam source to a piping (15a) through which said preheating source medium flows, a flow control valve (21c) is provided for controlling the flow rate of said preheating source medium to be extracted out of the system, a flow control valve (21d) is provided for controlling the flow rate of a heating steam to the evaporator (14), a temperature sensor (22a) is provided in a piping (13b) for leading emulsified fuel (11a) from the preheater (13) to the evaporator (14) at an outlet of the preheater (13) or at the inlet of the evaporator (14), a temperature sensor (22b) is provided in the piping (14d) from the evaporator (14) to the separator (15), a pressure sensor (23a) is provided in the piping (15a) through which said preheating source medium flows, wherein said flow control valves (21a-d) are operatable in response to signals from said temperature sensors (22a,b) and said pressure sensor (23a) such that the outlet temperature of said preheater (13) or inlet temperature of said evaporator (14) is controlled to be constant, the pressure in the preheating source medium supply piping (15a) for leading said preheating source medium into said preheater (13) is controlled to be constant, and the temperature difference of the outlet temperature relative to the inlet temperature of said evaporator (14) is controlled to be constant. A heavy oil emulsified fuel evaporator system as claimed in claim 3, characterized in that a construction (31) adapted to store the emulsified fuel of an increasable amount, as preheated, is provided in said preheater (13) or between said preheater (13) and said evaporator (14). A heavy oil emulsified fuel evaporator system as claimed in claim 4, characterized in that said construction comprises a buffer tank (31) provided in the piping (13b) for leading emulsified fuel (11a) from the preheater (13) to the evaporator (14).

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