Burner Nozzle and Coal Gasifier FIELD OF THE TECHNOLOGY [0001] The present invention relates to technology of combustion equipment structure, in particular relates to a burner nozzle. In addition, the present invention further relates to a coal gasifier provided with the above burner nozzle. BACKGROUND [0002] A burner nozzle is a conventional combustion component, which is widely used in various combustion equipments such as engine, boiler, coal gasifier etc. [0003] A typical structure of the burner nozzle is shown in Fig. 1, the burner nozzle comprises a nozzle housing 10 having a substantially cylinder shape, a fuel pipe 20 and a combustion-supporting gas pipe 30 are disposed in the nozzle housing 10, the fuel which passes through the fuel pipe 20 and the combustion-supporting gas which passes through the combustion-supporting gas pipe 30 are mixed at an end of the burner nozzle, and are ignited to form flame. According to the gas compositions of different combustion-supporting gas, the burner nozzle can be divided into three types, which are air combustion-supporting type, oxygen-enriched combustion-supporting type and pure oxygen combustion-supporting type. The oxygen content of the combustion-supporting gas in an oxygen-enriched combustion-supporting type nozzle is above 20%, pure oxygen combustion-supporting type nozzle adopts combustion-supporting gas with oxygen content above 99%. [0004] For the burner nozzle of above structures, when adopting dry pulverized coal as the fuel, usually adopting nitrogen as the carrying gas, the high flow rate carrying gas, which carries the dry pulverized coal, is jet out from an front end of the burner nozzle, such that to mix with the combustion-supporting gas and ignite thereof. The defect existed in the dry pulverized coal burner nozzle is, the friction force of the high flow rate dry pulverized coal is high, which brings serious wear to the end of the burner nozzle, thus affecting the service life of the burner nozzle. [0005] In order to overcome this defect, the prior art provides a solution, which refers to a Chinese patent application with the application number 200620045550.6. In the technical scheme, a central pipe which discharges fuel is a little bit lower than an annular pipe which discharges combustion-supporting gas. [0006] However, the above technique still exists the following defect: the discharged high-speed combustion-supporting gas will entrain the discharged dry pulverized coal, and the dry pulverized coal brings serious wear to the end of the flowing pipe of the 1 6799028_1 (GHMatters) P96069.AU DENISET combustion-supporting gas. SUMMARY [0007] Embodiments of the present invention may provide a burner nozzle and a coal gasifier so as to solve the defect in prior art, which may avoid the end of the combustion-supporting gas pipe from being worn, and may increase the service life of the burner nozzle and the coal gasifier. [0008] A first aspect of the present invention provides a burner nozzle, comprising a nozzle housing, a fuel pipe and a combustion-supporting gas pipe are provided in the nozzle housing, the combustion-supporting gas pipe is disposed around the outside of the fuel pipe, an outlet end of the combustion-supporting gas pipe extends forward than an outlet end of the fuel pipe, a separating pipe is provided in the combustion-supporting gas pipe, which separates the combustion-supporting gas pipe as a first combustion-supporting gas pipe and a second boundary gas pipe, wherein the second boundary gas pipe is deposited around the outside of the first combustion-supporting gas pipe, and the outlet end of the fuel pipe extends forward than an end of the separating pipe; wherein, the end of the separating pipe is provided with a flow baffling ring, the flow baffling ring is connected with an outer wall of the separating pipe, and protrudes towards the second boundary gas pipe. [0009] Preferably, the outlet end of the combustion-supporting gas pipe has a convergent portion; the end of the separating pipe extends forward than an initiating end of the convergent portion. [0010] Preferably, the sectional area at the outlet of the second boundary gas pipe is smaller than the sectional area in the interior of the second boundary gas pipe. [0011] The end of the separating pipe is provided with a flow baffling ring, the flow baffling ring is connected with an outer wall of the separating pipe, and protrudes toward the second boundary gas pipe. [0012] Preferably, the outer wall of the fuel pipe has a protrude structure provided adjacent to the outlet end. [0013] Preferably, the second boundary gas pipe is communicated with a vapour pipe, which supplies vapour into the second boundary pipe. [0014] Another aspect of the present invention further provides a coal gasifier, which comprises the burner nozzle of the first aspect. [0015] In an embodiment of the present invention, since the separating pipe is provided in the combustion-supporting gas pipe, the separating pipe separates the combustion-supporting gas 2 6799028_1 (GHMatters) P96069.AU DENISET pipe as a first combustion-supporting gas pipe and a second boundary gas pipe, in application process, the fuel is supplied from the fuel pipe, and the combustion-supporting gas is supplied from the first combustion-supporting gas pipe and the second boundary gas pipe at the same time, the combustion-supporting gas in the second boundary gas pipe can form a boundary film on the inner wall of the outlet end of the second boundary gas pipe, which protects the outlet end, such that to avoid the combustion-supporting gas pipe from being worn by the fuel jet out from the fuel pipe, thus increasing the service life of the nozzle. BRIEF DESCRIPTION OF THE DRAWINGS [0016] Embodiments of the invention and other embodiments will now be described, by way of example only, with reference to the accompanying non-limiting Figures, in which: [0017] Fig. 1 is a schematic structural diagram of a typical burner nozzle in prior art; [0018] Fig. 2 is a schematic structural diagram of a burner nozzle provided by a first embodiment; [0019] Fig. 3 is a schematic structural diagram of a burner nozzle provided by a second embodiment. [0020] Reference signs: [0021] 10 - nozzle housing; 20 - fuel pipe; 21 - protrude; [0022] 31 - first combustion-supporting gas pipe; 32 - second boundary gas pipe; [0023] 33 - convergent portion; 40 - separating pipe; 41 - flow baffling ring. DETAILED DESCRIPTION [0024] In order to make the purposes, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be described more clearly and completely in combination with the drawings of the embodiments of the present invention. Obviously, the embodiments described here are a part of the embodiments of the present invention but not all of the embodiments. All other embodiments, which can be derived by persons skilled in the art from the embodiments given herein without creative work, shall fall within the protection scope of the present invention. [0025] Now referring to Fig. 2, a schematic structural diagram of a burner nozzle provided by a first embodiment. [0026] In a first embodiment, a burner nozzle comprises a nozzle housing 10, a fuel pipe 20 and a combustion-supporting gas pipe 30 are provided in the nozzle housing 10, the combustion-supporting gas pipe 30 is disposed around the outside of the fuel pipe 20, an outlet 3 6799028_1 (GHMatters) P96069.AU DENISET end of the combustion-supporting gas pipe 30 extends forward than an outlet end of the fuel pipe 20. [0027] A separating pipe 40 is provided in the combustion-supporting gas pipe 30, which separates the combustion-supporting gas pipe 30 as a first combustion-supporting gas pipe 31 and a second boundary gas pipe 32 with annular shape, the second boundary gas pipe 32 is formed at the outside of the first combustion-supporting gas pipe 31, the outlet end of the fuel pipe 20 extends forward than an end of the separating pipe 40. [0028] The burner nozzle provided by the present embodiment, since the separating pipe 40 is provided in the combustion-supporting gas pipe 30, the separating pipe 40 separates the combustion-supporting gas pipe 30 as a first combustion-supporting gas pipe 31 and a second boundary gas pipe 32, in application process, the fuel is supplied from the fuel pipe 20, and the combustion-supporting gas is supplied from the first combustion-supporting gas pipe 31 and the second boundary gas pipe 32 at the same time, the combustion-supporting gas in the second boundary gas pipe 32 can form a boundary film on the inner wall of the outlet end, which protects the outlet end of the second boundary gas pipe 32, such that to avoid the boundary gas pipe 32 from being worn by the fuel jet out from the fuel pipe 20, thus increasing the service life of the nozzle. [0029] On the basis of the burner nozzle provided by the first embodiment, a further improvement can be made, the detailed improvement scheme is as follows: [0030] The outlet end of the combustion-supporting gas pipe 32 has a convergent portion 33; the end of the separating pipe 40 extends forward than an initiating end of the convergent portion 33. [0031] The burner nozzle provided by the present embodiment, since the combustion-supporting gas pipe 32 has a convergent portion 33, when the combustion-supporting gas in the second boundary gas pipe is jet out, the combustion-supporting gas changes its direction at the initiating end of the convergent portion 33 towards the second boundary gas pipe 32, thus the boundary film formed on the inner wall of the convergent portion 33 becomes thicker, which provides better protection to the inner wall of the outlet end of the fuel pipe 30. [0032] In addition, on the basis of the burner nozzle provided by the above embodiment, the sectional area at the outlet of the second boundary gas pipe 32 can further be set to smaller than the sectional area in the interior of the second boundary gas pipe 32, specifically, the sectional area of the outlet formed by the end portion of the separating pipe 40 and the convergent portion 33 can be designed to smaller than the sectional area of the interior of the second boundary gas 4 6799028_1 (GHMatters) P96069.AU DENISET pipe 32, by adopting said designing scheme, the outlet of the second boundary gas pipe 32 is smaller than the interior size, thus a high flow rate boundary film is formed on the inner wall of the second boundary gas pipe, the boundary film provides better protection to the outlet end of the fuel pipe 30. [0033] Now referring to Fig. 3, a schematic structural diagram of a burner nozzle provided by a second embodiment. [0034] The difference between the burner nozzle provided by the present embodiment and the burner nozzle in above embodiment is, a flow baffling ring 41 is provided at the outlet of the separating pipe 40, the flow baffling ring 41 is connected with the outer wall of the separating pipe 40 and protrudes towards the second boundary gas pipe 32. [0035] The burner nozzle provided by the present embodiment, since the flow baffling ring 41 is provided on the outer wall of the outlet of the separating pipe 40, the flow baffling ring 41 provides the effect of flow limit and direction changing to the combustion-supporting gas in the second boundary gas pipe 32, which can form a high flow rate boundary film on the inner wall of the combustion-supporting gas pipe 30, thus providing better protection to the outlet end of the fuel pipe 30. [0036] In addition, as shown in Fig. 1 and Fig. 2, in the burner nozzles provided by above all embodiments, a protrude 21 is provided on the outer wall of the fuel pipe 20 adjacent to the outlet end, specifically, the protrude 21 can be a protrude 21 circumferentially along the outer wall of the fuel pipe 20, the section of the protrude 21 is a triangle with smooth transition, which guarantees a sufficient mixing of the fuel and the combustion-supporting gas in the combustion-supporting gas pipe 30, and is beneficial to a sufficient burning of the fuel. [0037] It should be noted that, the burner nozzle provided by the above embodiment supplies combustion-supporting gas in the first combustion-supporting gas pipe 31 and the second boundary gas pipe 32 at the same time, or can supply combustion-supporting gas in the first combustion-supporting gas pipe 31 and supply other gas in the second boundary gas pipe 32, such as vapour, to form the boundary film. [0038] An embodiment further provides a coal gasifier, which comprises the burner nozzle provided by any of the embodiments of the present invention, which can avoid the combustion-supporting gas pipe from being worn by the fuel jet out from the fuel pipe, such that to increase the service life of the nozzle. [0039] Finally, it should be noted that the above embodiments are merely provided for describing the technical solutions of the present invention, but not intended to limit the present invention. It should be understood by those of ordinary skill in the art that although the present 5 6799028_1 (GHMatters) P96069.AU DENISET invention has been described in detail with reference to the foregoing embodiments, modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent replacements can be made to some technical features in the technical solutions, as long as such modifications or replacements do not cause the essence of corresponding technical solutions to depart from the scope of the present invention. [0040] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. [0041] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 6 6799028_1 (GHMatters) P96069.AU DENISET