Apparatus for handling ammonia-containing acid gas streams
Unite Sttes Palm et a1.  
 atent [1 1 1 Apr. 15, 1975 1 APPARATUS FOR HANDLING AMMONIA-CONTAINING ACID GAS STREAMS [75] Inventors: John W. Palm; Kay L. Berry, both of Tulsa, Okla.  
 [73] Assignee: Amoco Production Company, Tulsa,  
 Okla.  
 [22] Filed: Feb. 26, 1973 [21] Appl. No.: 335,615  
 [52] US. Cl 23/262; 23/255 R; 423/574; 431/76 [51] Int. Cl C01b 17/04; F23n 3/00; F23n 5/00 [58] Field of Search. 23/262, 277 R, 254 R, 255 R, 23/232 R, 230 A, 253 A; 423/573, 576, 574;  
 [56] References Cited UNITED STATES PATENTS 1,710,772 4/1929 Hepburn 431/76 X 2,834,653 5/1958 Fleming et aI. 423/576 2,834,655 5/1958 Chute et aI. 23/262 X 2,892,684 6/1959 King 23/230 A 2,945,748 7/1960 Magill 23/262 X 3,026,184 3/1962 Karasck 423/573 X 3,297,409 l/l967 Kunkel et al. 423/574 VAPOR TO T CATALYTIC REACTOR NH3-FREE ACID GAS LIQUID SULFUR 3,773,912 11/1973 Spanglcr, Jr. 423/574 3,819,816 6/1974 Wundcrlich et a1. 423/573 X 3,822,337 7/l974 Wundcrlich et a1. 423/574 X Primary E.\&#39;aminer.loseph Scovronek Assistant E.raminerBarry l. Hollander Attorney, Agent, or Firm-Arthur Mcllroy; Paul F. Hawley [57] ABSTRACT Refinery or similar streams containing NH are processed in a sulfur plant having separate burners for the Nl-l -containing acid gas stream and for the NH -frce acid gas stream. A sampling device is provided for continuously or periodically sampling the combustion products from the unit burning the NH -containing gas. The H S/SO ratios at this sample point and in the sulfur plant tail gas are used to control the operation of the system.  
 The present invention relates to the conversion of H S to elemental sulfur. More particularly, it is concerned with the use of an H S-containing stream as a partial source of sulfur recovery plant feed wherein said stream has been derived, for example, from refinery processes involving the treatment of sulfurand nitrogen-containing compounds with hydrogen.  
 6 Claims, 2 Drawing Figures ACID GAS CONTAINING NH BOILER AND CONDENSER PAIENIEDAPR 1 1915 3.877. 879  
 &#34;ACID GAS CONTAINING NH BOILER AND CONDENSER 38 VAPOR TO CATALYTIC REACTOR ACID GAS HG. 2  
  APPARATUS FOR HANDLING AMMONIA-CONTAINING ACID GAS STREAMS BACKGROUND OF THE INVENTION In many catalytic hydrogenation processes applied to hydrocarbon oils, shale oil, tar sands, etc., of which hydrocracking and hydrotreating or hydrodesulfurization are typical examples, H 8 and NH are produced as a result of reaction of hydrogen with sulfur compounds and nitrogen compounds contained in the oil. Sometimes, this conversion of one or the other or both of the sulfur and nitrogen compounds is the desired reaction, while in other cases it is merely an incidental reaction. Normally, in a typical process, liquid hydrocarbon oil containing nitrogen compounds and sulfur compounds and recycle hydrogen-rich gas and makeup hydrogen are passed through a reaction zone, usually containing a catalyst, at elevated temperature and pressure at which at least a portion of the hydrocarbons are vaporized; and there is obtained as a reaction zone effluent a mixture of vaporized hydrocarbons, hydrogen, H 5 and NH;,. The effluent may also contain heavier hydrocarbons which are liquid at the reaction conditions. The reaction effluent is cooled to condense vaporized hydrocarbons, whereby the liquid hydrocarbons can be separated from the hydrogen-rich recycled gas, which is then reused in the hyrodgen process.  
  When the reaction effluent contains both H 3 and NH;,, it has been found that on cooling to temperatures below about 300F, the H 8 and the NH;; may react to form salts which sometimes cause clogging problems in the heat exchangers and the lines. Injection of water into the reaction effluent upstream of the heat exchangers has been used to wash out such deposits and- /or to prevent their formation. This water injection can provide a means of removing much of the ammonia formed if rather large amounts of water are injected sufficient to dissolve the ammonia.  
  While there are a number of known methods for separating mixtures of NI-I and H 8 from the aforesaid effluent, most of such methods involve scrubbing the gaseous phase produced in the hydrogenation step mentioned above with water. The resulting foul water stream contains primarily H 5 and N11 both of which can be recovered from said foul water stream by subjecting the latter to steam stripping or the equivalent.  
  For conservation and ecological reasons, it is desirable to recover both H 8 and NH;, in useful form. Methods are known by which it is possible to separate the NH from H 8; however, in many instances, operators do not find it economically justifiable to do so and dispose of such mixtures of H 8 and NI-l as a partial feed stream to a sulfur recovery unit. Uncontrolled operation using a stream of this kind of mixed feed has led to difficulties because the conditions used for combustion of H 8 to produce sulfur do not favor complete combustion of NH Even if only relatively small quantities, e.g., 200 ppm of NI-I remain in the combustion effluent gas which passes through the system, the presence of NH in such amounts constitutes a hazard because of its ability to react with S0 to form ammonium sulfate at numerous locations in the plant and plug flow lines, seal pots, etc.  
 SUMMARY OF THE INVENTION We have now discovered that sulfur plants using feed streams containing NI-I can be operated smoothly by LII employing a separate muffle furnace for combustion of the H SNH mixture derived from the aforesaid foul water stream. This mixture generally constitutes from about 3 to about 30 volume percent of the total feed to the plant; however, the percentage may be even higher in some plants. A second and usually larger muffle furnace is used for combustion of the essentially NH free H 8 stream. This invention makes it possible to closely control the conditions for combustion of the ammonia, in order to achieve optimum combustion.  
  During operation the air rate to the burner in the first furnace is adjusted based on continuous or frequent sampling of the first burner effluent to determine the H S/SO ratio. This, along with monitoring the H S/SO ratio in the plant effluent, aids in maintaining the unit at optimum operating conditions. Generally, it is desirable to supplement the H 8 in the NH,, containing feed stream with H S from the NH --free stream in order to maintain the desired temperature in the first muffle furnace. Because the sulfur and nitrogen content of crudes used in refineries is often subject to wide variation, it will be apparent that both the amount and proportion of the l-l- S and NH produced during hydrogenation of the crude can fluctuate substantially. These fluctuations contribute to the problems caused by in-- complete combustion of the ammonia. Our invention overcomes these problems by maintaining a suitable atmosphere for combustion of the ammonia.  
 DESCRIPTION OF DRAWINGS AND A PREFERRED EMBODIMENT Our invention will be further illustrated by reference to the accompanying drawings in which:  
  FIG. 1 is a combination diagrammatic and sectional view of an embodiment employing separate muffle furnaces that discharge into separate boiler sections, with a gas sampling line placed in direct communication with the discharge end of the boiler section taking combustion products from the smaller of the two furnaces.  
  FIG. 2 illustrates another embodiment in which a single muffle furnace is equipped with two burners separated from one another by a refractory barrier or partition so that no substantial mixing of the combustion products therefrom occurs upstream of the sampling point.  
  In FIG. 1, NI-l -free acid gas is introduced into burner 2 via lines 4 and 6 and mixed with air entering through line 8. Combustion products exhaust into muffle furnace l0 producing a temperature therein in the range of about 2000 to 2600F. The Mi -containing H 5 stream is sent to burner 12 via lines 14 and 16 where it is mixed with air entering by means of line 18. Typically, the latter stream contains about 33 mol NH 33 mol H 8, 33 mol H 0, and small amounts of hydrocarbons. In order to assure essentially complete combustion of Nl-l to N and H 0 in muffle furnace 20, the temperature therein should be maintained at a minimum of 2500 to 2600F. We have found that, at temperatures of 2500F and 2600F, the amount of NH in the furnace product is about 150 and about ppm by volume, respectivelyconcentrations well within the permissible range. These temperatures can be employed without requiring a special refractory. Higher temperatures can, of course, be used but the refractory requirements are more severe. The temperatures existing in furnaces l0 and 20 are determined by means of indicators 24 and 26, respectively.  
  throughlines I4 and 22 is transformed into S and minimum concentrations of NH, and S0 are achieved.  
  In furnace a substantial amount, e.g., 40 to 60%, of the H 5 is converted to sulfur. A smaller percent conversion to sulfur occurs in furnace 20. This sulfur along with water vapor, nitrogen. and unconverted H 5 and S0 are discharged into a combination boiler and condenser unit, 28, maintained at a temperature of about 300 to about 400F. The elemental sulfur produced in furnaces l0 and is conducted through tubes and 32, respectively. and then along with unreacted H 5 and S0 is discharged into refractory lined chamber 34 and thereafter withdrawn therefrom via cooling tubes 36 located in the lower part of boiler 28. Tubes 36 discharge into chamber 38 where liquid product sulfur is separated from H 8, S0 water vapor, and inerts which exit through line 40 while sulfur is removed by means of line 42.  
  If desired, the gases in line 40 may be preheated by any of several known methods to a reaction temperature of about 425 to 450F and conducted to a series of catalytic reactors (not shown) where elemental sulfur is formed in a known manner.  
  In operation of the unit shown. it is important that the gases discharged from tubes 32 into chamber 34 be sampled and analyzed to determine the H S/SO ratio. This is accomplished by periodically or continuously withdrawing a small stream from the upper part of chamber 34 via sample line 44. We have found that at an &#34;ins/so, ratio of 0.086 the equilibrium ammonia content in the gas leaving muffle furnace 20 is less than one-third of the value which exists at an H S/SO ratio of 2.0. However, the equilibruim S0 increases as the H S/S0 ratio is decreased. Periodically, the gas withdrawn through sample line 44 is analyzed for NH and S0 as well as for H 8 and S0 while the air rate in line 18 is varied. This will show the optimum H S/SO- ratio which should be maintained during continuous operation. The air rate in line 8 is controlled to maintain the H S/S0 ratio in the sulfur plant tail gas within the desired limits.  
  In FIG. 2, muffle furnace 50 is equipped with separate burners, 52 and 54, supplied, respectively, with NH -free acid gas in line 56 and with NH -containing acid gas in line 58. The furnace itself is constructed of a metal shell, 60, having on the interior thereof a refractory lining, 62. Significant mixing of combustion products from burners 52 and 54 is prevented by means of partition 64, which divides muffle furnace 50 into separate combustion zones 68 and 70. A sampling means, 66, is inserted into the furnace downstream of burner 54 in order to withdraw combustion products to determine whether the NH;, fed to the system is being consumed to the proper extent. Downstream of sample point 66, the effluent from chamber 70 combines with the effluent from chamber 68 to permit formation of additional elemental sulfur in chamber 72.  
  An arrangement of the type shown in FIG. 2 results in a slightly greater conversion of H 5 to sulfur in the combined furnaces, than occurs in the furnace arrangement of FIG. 1. The products of combustion are discharged from furnace chamber 72 directly into a conventional waste-heat boiler (not shown). Any sulfur liquefied at this stage can be withdrawn, the uncondensed effluent adjusted to a temperature of about 425 to 450F, and the H S-SO mixture contained therein converted over a bauxite or similar catalyst to free sulfur in a known manner.  
 We claim:  
  1. In an apparatus for the preparation of elemental sulfur from gases containing H S and NH the improvement comprising the combination of two separate combustion chambers of different size in parallel, separate means for injection of air and of ammoniacontaining H 5 into the smaller of said chambers and separate means for injecting an NH -free stream of H S and of air into the other of said chambers, means for sampling the products of combustion from the smaller of said chambers, means for determining the H S/SO ratio in the sample, means for regulating the air to said smaller chamber based on the H S/S0 ratio determined, and an enclosed vessel having &#39;a boiler section into which said chambers discharge.  
  2. The apparatus in claim 1 in which said chambers are within a second enclosed metal vessel.  
  3. The apparatus in claim 1 in which said chambers discharge into separate boiler sections in said enclosed vessel and said sampling means is located at the disdense the sulfur vapor discharging from both of said boiler sections.  
 6. The apparatus in claim 2 wherein said chambers are separated by means of a refractory partition.