Apparatus and process for airheater without quench in carbon black production

Abstract

In the production of carbon black by the furnace process, fuel and heated combustion air or oxygen enriched air from the combustion air heat exchanger, are fired into the reactor, resulting in a hot flame. Carbonaceous feed stock, injected into this hot flame containing considerable excess oxygen, is pyrolized. The effluent from the reactor reaction zone is quickly cooled, typically by water quench, to prevent secondary reactions that decrease the quality and yield of carbon black. In the present invention, water quench is eliminated and the effluent from the reaction zone passes directly into the metallic combustion airheater, quickly cooling it to stop pyrolysis and heating the combustion air to typically 950 C. The combustion air heater is smaller due to high heat flux per unit volume. Further cooling of the effluent to the carbon black collector, is achieved by series of heat exchangers and trimming water quench.

Claims

1. A carbon black process system comprising a fuel combustion zone, carbon black reactor and an improved combustion air heater constructed and arranged to stop pyrolysis within the carbon black reactor by indirect heat transfer by said combustion air heater; wherein fuel is burned in said combustion zone to produce hot combustion gases, said combustion gases is reacted with a carbon feedstock to produce a hot effluent stream which flows through said improved combustion heater consisting of a double plate tube sheet at said combustion air heater hot effluent entry, a single plate tube sheet at said combustion air heater cooled effluent exit; further comprising a plurality of metallic tubes in operative connection to the said tube sheets and a metallic shell enclosing the said tube sheets and tubes forming the shell space for the flow of said combustion air; wherein said hot effluent from said reactor enters said combustion air heater through the inside of said plurality of tubes connected to said double plate tube sheet and exiting said combustion air heater apparatus through tubes connected to said single plate tube sheet in operative connection with downstream effluent cooling equipment; said combustion air heater stream flows in multiple passes over the outside of the tubes in the shell space of said apparatus transferring the heat from said hot reactor effluent to said combustion air and wherein individual replaceable tube seals are located at the top tube sheet allowing thermal expansion of the hot tubes and preventing hot combustible reactor effluent stream mixing with the said combustion air.

2. In the combustion air heater apparatus as claimed in claim 1, the combustion air is divided into three streams; a first stream comprising of 50% of the total combustion air; a second stream comprising of 35% to 40% of the total combustion air and a third stream comprising the balance of the total combustion air.

3. In the combustion air heater apparatus as claimed in claim 1, the said first combustion air stream enters the shell space near the said double plate tube sheet and flows over the outside of the said plurality of tubes in multiple passes co currently to the hot effluent which is flowing inside the said plurality of tubes; wherein the said second stream of combustion air enters the said shell space near the said single plate tube sheet and flows over the said plurality of tubes in multiple passes, counter currently to the hot effluent flowing inside the said plurality of tubes; segmented, disc and donut or similar baffles located in the said shell space of the said combustion air heater apparatus facilitate theses multiple passes for the combustion air streams.

4. In the combustion air heater apparatus as claimed in claim 1, the third combustion air stream enters the space between the plates of the said double plate tube sheet by means of multiple nozzles, thereby cooling the two plates of the said double plate tube sheet from the heat of the said plurality of tubes in which the hot effluent is flowing and from the radiation heat of the carbon black reactor; after cooling the said double plate tube sheet, the said third stream of combustion air will exit the top plate of the said double plate tube sheet and flow towards the said single plate tube sheet through one or more tubes, co currently to the hot effluent flowing inside said plurality of tubes; this third stream will then join the said second stream of air and flow over the outside of the plurality of tubes co currently to the hot effluent flowing inside said plurality of tubes; the said combustion air stream 1 and said combustion air streams 2 and 3, after absorbing the heat from the hot effluent flowing inside the said plurality of tubes, exit the said combustion air heater apparatus near the middle of the shell.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows the General arrangement of the present invention, indicating the flow of the carbon black effluent from the reaction zone and the 3 streams of the combustion air through the combustion air heater, NOAPH FIG. 1A shows schematic of Carbon Black Manufacturing Process.

(2) FIG. 2 depicts the cooled double bottom tube sheet of the invention, showing the flow of the air stream 3, tube sleeves and their attachment to the tube sheet plates and attachment of the tubes to the tube sleeves.

(3) FIG. 3 depicts the sliding type seal between the tube and the top tube sheet

(4) FIG. 4 depicts the bellows type of seal between the tube and the top tube sheet, bellows in compression during service

(5) FIG. 5 depicts the bellows type of seal between the tube and the top tube sheet, bellows in tension during service

(6) FIG. 6 depicts the temperature profile for the tube and shell of the present invention, also showing temperature profiles for the prior art

(7) FIG. 7 depicts the thermal expansion profile of the tube and shell of the present invention, also showing the thermal expansion profile for the prior art.

(8) FIG. 8 (New) depicts the quench water flow and irrecoverable energy loss due to quench water

DESCRIPTION

(9) The invention is depicted in FIG. 1:

(10) A is the entry of the Carbon black furnace effluent into the apparatus.

(11) B is the exit of the effluent after being cooled in the apparatus

(12) 1 is the first stream of process air, entering at the hot end of the air heater through nozzle 12.

(13) 2 is the second stream of process air, entering at the colder end of the air heater through nozzle 13.

(14) 3 is the third stream of process air, entering from the cooling air header 7 into the double plate bottom tube sheet, 4, entering through cooling air nozzles 15. The bottom plate of this tube sheet

(15) 4 is refractory lined to protect this plate from the high temperature of the reactor effluent.

(16) 5 are the multiple tubes of the airheater inside which the hot reactor effluent flows at high velocity. These tubes are connected to the bottom tube sheet 4 and the top tube sheet 6. This top tube sheet 6 is generally refractory lined

(17) 8 is the metallic shell of the airheater, fitted with internal insulation 10, retained by metallic pins and metallic plate 9. External insulation on the shell is shown as 11.

(18) 14 is the nozzle through which the heated process air stream leaves the airheater.

(19) 16 is the return pipe for the cooling air from the top plate of the bottom tube sheet 4 to the colder section of the airheater. This can be a single large pipe or multiple smaller pipes.

(20) 17 are the set of baffles inside the airheater which makes the process air to flow in multiple passes over the outside of the tubes 5. These baffles may of the segmented type (shown) or the disc and donut type.

(21) Constant load hangers 19 or counter weights are provided to keep the shell always in tension and prevent shell buckling under adverse operating conditions.

(22) Sway brackets 20 are provided on the shell of the airheater to minimize the lateral movement of the airheater due to wind loads, uneven heating of the tubes 5, uneven cooling of shell due to changing wind direction.

(23) FIG. 2 shows the tubes 5 welded to sleeves 18 which is welded to the bottom tube sheet 4 and shows the tube to sleeve weld.

(24) The tubes 5 may be connected to the top tube sheet 6 with packing seals 21 (FIG. 3), bellows type seals 22 (FIGS. 4 & 5) or any other suitable method of sealing the process air from mixing with the hot combustible reactor effluent.

(25) FIG. 3 shows the packing seal type of joint. The packing seal 21 is provided with grooves and ceramic packing to let the tube freely expand inside the packing seal, at the same time making a difficult path for the air inside the shell to leak into the hot smoke. The tube end is machined to close tolerance with a very small clearance between the tube and the seal. When the hotter tube expands in diameter more than the colder seal, the clearance becomes smaller and the air to smoke seal tighter. A threaded follower 22 keeps the ceramic packing tight as a secondary sealing.

(26) FIG. 4 shows a replaceable bellows type seal joint 23, with bellows in compression during service. This seal has an inner tube 24 (welded to the tube 5), outer specially shaped tube 25, multi convolution metallic bellows 26, connected by welding to 24 and 25. Ceramic packing made out of ceramic rope 27 is placed tightly between 24 and 25 to minimize the ingress of carbon black in the smoke getting to the inside of the bellows. Such ingress over a period of time will pack the bellows with hardened carbon black and make the bellows ineffective, as the bellows squeeze together during service. The ceramic rope is kept in place by the retainer ring 28. The entire joint is connected to the top tube sheet 6 by welding to the tube sheet sleeve 29. The thin walled bellows are protected from the turbulence of the flowing process air by the bellows cover 30.

(27) FIG. 5 also shows a replaceable bellows type seal joint 31, but it is designed for the bellows to be in tension in service. This type of joint is less sensitive to carbon black packing inside the bellows. When in service, the bellows stretch and the joint is still effective. This seal has an outer tube 24 (welded to the tube 5), inner specially shaped tube 25, multi convolution metallic bellows 26, connected by welding to 24 and 25. Ceramic packing made out of ceramic rope 27 is placed tightly between 24 and 25 to minimize the ingress of carbon black in the smoke getting to the inside of the bellows. The ceramic rope is kept in place by the retainer ring 28. The entire joint is connected to the top tube sheet 6 by welding to the tube sheet sleeve 29. No separate bellows cover is needed as the outer tube 24 protects the thin walled bellows from the turbulence of the flowing process air.

(28) FIG. 6 shows the tube and shell metal temperature profile of the invention, NQAPH and the prior art combustion airheater APH. It should be noted that the maximum tube wall and shell temperatures occur near the air outlet near the middle of the airheater (NQAPH). At the smoke entry and exit points of the present invention, (NQAPH), where the tubes are connected to the bottom and top tube sheets respectively, the temperatures are lower, making the joints stronger and less susceptible to failure.

(29) FIG. 7 shows the thermal expansion of the tubes, the shell and the differential thermal expansion between the tube and shell for the NQAPH and prior art combustion airheater APH. It should be noted that the thermal expansions are smaller for the present invention than the prior art airheater. The differential expansion between the tube and shell is also smaller for the present invention, resulting in smaller number of convolutions for the bellows type seal depicted in FIGS. 4 and 5. The lower thermal expansions are due to the shorter length of the tubes in the present invention (NQAPH) as shown in Table 1.

(30) FIG. 8 (New) shows the quench water flow and irrecoverable energy loss associated when quench water is used to stop pyrolysis and also cool the effluent safe enough for downstream equipment. The present invention, NQAPH eliminates water quench and saves water and energy.

EXAMPLE

(31) In a carbon black furnace, 17,000 nm3/h of hot air at 920 C is admitted along with adequate fuel (oil or natural gas) into the reactor to raise the flame to a temperature around 1925 C. Hot carbonaceous feed stock is sprayed into this Oxygen rich hot flame and the ensuing pyrolysis converts the feed stock to carbon black and other gases. This reactor effluent of 29,130 nm3/h at around 1300 C, enters the present invention combustion air heater, NQAPH, which stops the pyrolysis and also preheats the combustion air to 950 C. In the prior art APH, with counter current flow of effluent and combustion air, 1300 C+ effluent temperature is too high and the effluent is cooled down to 1050 C by water spray of 2,750 kg/h, before entering the APH. The volume of gases entering the APH is 32,550 nm3/h. This water (2,750 kg/h) is not recovered and will be lost into the atmosphere. This additional water also causes problems in the downstream equipment like the bag filter with wetness.

(32) In the present invention of combustion airheater (NQAPH), all of this water is saved. A single airheater (NQAPH) will stop the pyrolysis and cool the gases from 1,300 C to 865 C, while heating the combustion air to 950 C. Further heat recovery from the CB containing reactor effluent down to the safe temperature for the Carbon Black collector can be achieved with additional heat exchangers for heating feed stock and fuel, high and low pressure steam generation, tail gas preheating etc.

(33) Table 1 compares the airheater (NQAPH) and the prior art airheater (APH), both of them designed to preheat the process air to 950 C.

(34) TABLE-US-00001 TABLE 1 NQAPH APH Process Data: Heating side: Medium CB gases CB gases Volume of gases nm.sup.3/h 29,130 32,550 Temperature of gases entering C. 1,300 1,050 Temperature of gases leaving C. 865 640 Heat Transferred MM Kcal/h 5.126 5.126 Entering velocity inside tubes m/s 90.7 79.7 Exiting velocity inside tubes m/s 65.6 54.5 Additional Quench water kg/h 0 2,750 Cooling side: Medium Process Air Process Air Flow volume nm3/h 17,000 17,000 DBTS Cooling air flow nm3/h 1,700 1,700 Entering temperature C. 60 60 Exiting temperature C. 950 950 Heat Exchanger Data: Number of tubes 108 108 Tube spacing mm 130 130 Length of each tube m 9.33 12.5 Total Number of baffles 28 16 Heat flux_Co-current section kcal/m2 h 22,291 Heat flux_Counter- kcal/m2 h 15,390 13,600 current section Overall Heat Flux kcal/m2 h 18,223 13,600 Total Heating Surface m2 281.3 376.9 Tube thermal Expansion mm 142 188 Shell thermal expansion mm 106 128 Differential thermal mm 36 60 Expansion Effluent residence time sec 0.120 0.186