in order to make the structure and characteristics as well as the effectiveness of the present invention to be further understood and recognized , the detailed description of the present invention is provided as follows along with embodiments and accompanying figures . first , please refer to fig1 and fig2 , which show structural schematic diagrams according to the present invention . as shown in the figures , the structure of the hybrid heating apparatus comprises a tank 1 , a top opening part 11 , a bottom opening part 12 , a lid 2 , a plurality of holes 21 , at least an inner heating unit 3 , a gas distributor 4 , and an outer heating unit 5 . the top and bottom opening parts 11 , 12 are located on the top and bottom ends of the tank 1 . lid 2 is disposed on the top opening part 11 . the plurality of holes 21 are disposed on the surface of the lid 2 . in addition , the plurality of holes 21 have flanges 9 , respectively , used as the connecting members with the inner heating unit 3 . additionally , the inner heating units 3 insert into the plurality of holes 21 , respectively and enter downwards toward the inside of tank 1 . the gas distributor 4 is disposed at the bottom opening part 12 of tank 1 . the outer heating unit 5 surrounds and covers the outer sidewall of tank 1 . the technical feature of the present invention is to combine multiple heat sources for achieving the purpose of hybrid heating , and target to be heated by those various types of heat sources is placed in tank 1 . please refer again to fig1 and 2 . there is a storage space 13 in tank 1 used for accommodating the materials to be heated . the storage space 13 is formed by the sidewall and the bottom structure of the tank 1 . here , the materials to be heated are filters , which can be silica sand ( sio 2 ). these filter granules 7 are introduced into the storage space 13 via the filters inlet 22 on the lid 2 for heating . as storage space 13 is filled with a substantial amount of the filter granules 7 and heating is about to be performed , one of the heating sources heats by an electric heating apparatus and in the form of heat conduction . as shown in fig1 , the top opening part 11 of tank 1 is covered by lid 2 , which seals storage space 13 from the top direction . nonetheless , holes 21 are located on the surface of lid 2 so that the bar - shaped inner heating units 3 can insert through holes 21 , follow the direction guided by holes 21 , go down deep into storage space 13 , and then insert into filter granules 7 directly for transferring thermal energy by contacting them directly . the conduction thermal resistance r cd among filter granules 7 can be reduced effectively by distributing the electric heating bars . in addition , because multiple holes 21 can be disposed freely on the surface of lid 2 , users can decide the number of inserted inner heating units 3 and their distribution according to the requirements for adjusting and controlling the supply of thermal energy at will . moreover , in addition to the flexibility in the distribution of inner heating units 3 , the diameters of holes 21 can be varied as well . for example , the use of holes 21 having different diameters enables distributed usage of the inner heating unit 3 with different specifications . if there is any hole 21 having the flange 9 not inserted by the inner heating unit 3 , a blind flange 91 can be disposed for keeping its sealed . alternatively , devices such as a temperature measuring unit 33 can be inserted here according to the requirements for monitoring , and thus endow holes 21 with multiple functions . the length of inner heating unit 3 can also be adjusted according to the shape of storage space 13 . that is to say , a long heating unit 31 is selected for the deeper location in storage space 13 ; otherwise , a short heating unit 32 is adopted . by using this method of opening holes 21 on lid 2 and inserting inner heating units 3 for direct - contact heating , the heating uniformity can be ensured quite easily . in addition to inserting inner heating units 3 , another heat source according to the present invention comes from the periphery of tank 1 . as shown in fig1 , the outer sidewall of tank 1 is surrounded and covered by outer heating unit 5 , which is composed by at least an electric heating plate . opposed to inner heating unit 3 , outer heating unit 5 transfers thermal energy from outside of tank 1 to the inside . in addition to transferring thermal energy , the outer heating unit 5 also has the effect of the keeping constant temperature , and reducing the possibility of losing thermal energy from the inside of tank 1 by way of the sidewall and to the outside . in short , the technical characteristics of the disposition and distribution of the inner and outer heating units for providing direct - contact heating as described above is on improving the uniformity of the distribution of the supplied thermal energy and reducing the temperature variation in various regions in the storage space 13 . regarding the ratio of heat supply using the electric heater according to the present invention , inner heating unit 3 is the main supplier and provides a larger proportion of thermal energy , around 70 ˜ 90 % of thermal energy . the outer heating unit 5 is the supplementary supplier and supplying around 10 ˜ 30 % of thermal energy . it is because in addition to supplying heat into tank 1 , outer heating unit 5 is still possible to dissipate thermal energy outwards . thereby , the inner heating unit 3 is the main source of direct - contact heating due to the consideration of saving energy source . while using the electric heater to heat by direct contact uniformly , according to the present invention , hot exhaust gas a w is further used for forced convection in order to reduce the convection thermal resistance r cv and enhance the heating effect . in other words , external force , such as fans or pumps , is used for pushing and driving high - temperature gas to flow into the tank . in the present invention , the high - temperature exhaust gas a w used for heating is led in from the bottom of storage space 13 in tank 1 . the hot exhaust gas a w can be the exhaust gas generated by other apparatuses or system . therefore , it is not required to consume extra resources such as burning fuel for providing the high - temperature gas . instead , the exhaust gas once to be emitted directly to the atmosphere is recycled now through injected upwards from the bottom of storage space 13 . when hot exhaust gas a w flows upwards and passes the gaps among filter granules 7 , the heat convection coefficient h is increased by the flowing gas , which reduces the convection thermal resistance r cv and enhances the distribution uniformity of heat . as described above , the contact area of the interfaces between filter granules 7 is quite small and resulting in the problem of impedance in thermal conduction . regarding the method for reducing the thermal resistance , the present invention uses the forced convection of the hot exhaust gas a w to fill into the gaps among filter granules 7 . thus , the static gas in the gaps is pushed to move , which reduces the convection thermal resistance r cv and enhances the efficiency of heat transfer . the diameter of exhaust pipe 6 is normally smaller than the width of the tank 1 and limits the beneficial result of hot exhaust gas a w . in order to bring the gas flow and thermal energy into storage space 13 uniformly , the gas distributor 4 is disposed at the bottom opening part 12 of the tank 1 according to the present invention . the gas distributor 4 has a plurality of gas outlets 41 and hence guiding the heating gas upwards , namely , guiding the hot exhaust gas a w to storage space 13 . the purpose of gas distributor 4 is to diffuse the gas uniformly and let the gas flow into tank 1 in a large - area fashion . the structure of gas distributor 4 is full of variety instead of limited to a single specification . the top view shown in fig3 a and fig3 b show a simpler form of gas distributor 4 . gas outlets 41 and gas inlet zone 42 are disposed on the top and bottom surfaces of gas distributor 4 , respectively . at a center part , there is a filter outlet 15 allowing the heated filters to exit . the preferred disposition inside gas distributor 4 is diffusing the hot exhaust gas a w directly , which means after the hot exhaust gas a w enters the gas inlet zone 42 , it exits from gas outlets 41 dispersively and enters storage space 13 uniformly for heating filter granules 7 and reducing the thermal resistance . according to the present invention , gas distributor 4 with a specific vent or aperture ratio can be used according to the materials to be heated or other requirements . besides , the bore diameter of gas distributor 4 can be selected according to the size of the materials as well . take heating the silica sand for example . the diameter of the gas outlets 41 of the adopted gas distributor 4 is 2 mm , which is smaller than the diameters of the granules of the silica sand . therefore , the silica sand will not fall into the gas outlets 41 . furthermore , as shown in fig4 , gas outlets having a blocking - plate structure 43 can be selected as well . then , even if the diameters of filter granules 7 are smaller than the diameter of gas outlets 41 , under the protection of the blocking - plate structure 43 , filter granules 7 will not fall into gas outlets 41 easily . in addition , by the guidance of opening 431 of blocking - plate structure 43 , the hot exhaust gas a w will be guided with more flexibility . in addition to the above form of gas distributor 4 , it can be further designed to combine with the structure of tank 1 . in other words , the structure of gas distributor 4 is further extended into tank 1 , so that it is embedded inside tank 1 and attaches closely to the inner sidewall of tank 1 . then , in addition to entering storage space 13 upwards from bottom via a substantial amount of gas outlets 41 on the surface of gas distributor 4 , hot exhaust gas a w also enters storage space 13 from the side . therefore , the effect of forced convection of the hot exhaust gas a w is reinforced . please refer to fig5 a and 5b , which show another type of the gas distributor 4 for improving the thermal efficiency . a lining sheath 8 is further disposed in tank 1 . the shape of lining sheath 8 complies with storage space 13 . after the top of lining sheath 8 contacts the inner sidewall of tank 1 , a lining space 82 is formed between lining sheath 8 and tank 1 . besides , by removing gas distributor 4 , hot exhaust gas a w can enter storage space 13 , namely , lining space 82 , directly . after flowing upper by way of a plurality of gas injecting holes 81 on lining sheath 8 , hot exhaust gas a w exits by injection so that hot exhaust gas a w can flow from the edge close to the side of storage space 13 toward the center and thus fill the gaps among the interfaces of filter granules 7 more firmly . moreover , for the portion of tank 1 does not cover by outer heating unit 5 , as shown in fig6 , a portion of the sidewall of tanks 1 is a hollow layer 14 , which means thermal insulation can be achieved by vacuum . thereby , the thermal energy can be stored in storage space 13 . by using the structure design as described above , the hybrid heating apparatus according to the present invention combines various types of heat sources successfully for heating the materials in the storage space concurrently and ensures the materials can acquire uniform thermal energy . in addition , the heat supply of the heat sources can be controlled easily ; for example , by adjusting the length of the inserted inner heating unit and the flow rate of the hot exhaust gas . the present invention also promotes the concept of environmental protection . it recycles the exhaust heat generated by other apparatuses or systems directly by guiding and reduces the costs of energy consumption for the heating apparatus . in conclusion , having the advantages of considering thermal efficiency , heating uniformity , environmental protection , and power saving , the present invention undoubtedly provides a hybrid heating apparatus having economical and practical values . accordingly , the present invention conforms to the legal requirements owing to its novelty , nonobviousness , and utility . however , the foregoing description is only an embodiment of the present invention , not used to limit the scope and range of the present invention . those equivalent changes or modifications made according to the shape , structure , feature , or spirit described in the claims of the present invention are included in the appended claims of the present invention .