Abstract:
Method and system are presented for the combustion of hydrogen sulfide mixed with other gases for simultaneous recovery of sulfur and energy from hydrogen sulfide at higher efficiency. The amounts and velocity of the hydrogen sulfide into the reactor is selected in such a way that it is not possible to burn the hydrogen sulfide in a normal thin reaction zone during its combustion. The injected hydrogen sulfide gas is mixed in a thermal reactor with fresh air and hot active combustion gases in the reactor on account of internal jet pump effect and self-induced entrainment. The reaction is exothermic so that the chemical energy present in hydrogen sulfide is recovered together with the sulfur. Various reactors are shown capable of controlling the formation of a thermal distribution flow pattern based on the position, and position and direction (and other factors) regarding fluid introduction within a combustion chamber of the reactors.

Description:
PRIORITY 
     The present application claims priority to PCT International Application PCT/US2009/062758 filed on Oct. 30, 2009 which was published on Jun. 3, 2010 as Publication No. WO 2010/062682 A1. The PCT application claims priority from a U.S. provisional application filed on Nov. 3, 2008 titled “Efficiency Energy and Sulfur Recovery With Novel Isothermal Flame Reactor” and assigned U.S. Provisional Application Ser. No. 61/110,709; the entire contents of which are incorporated herein by reference. 
    
    
     PUBLISHED WORKS 
     The present application is directed to subject matter described in Sassi, M. and Gupta, A. K.: Sulfur Recovery from Acid Gases using the Claus Process and High Temperature Air Combustion (HiTAC) Technology, American Journal of Environmental Sciences, vol. 4, no. 5, 2008, pp. 502-511; the entire contents of which are incorporated herein by reference. 
     The present application is also directed to subject matter described in Selim, H., Gupta, A. K., and Sassi, M.: Acid Gas Composition Effects on the Optimum Temperature in Claus Reactor, 6 th  International Energy Conversion Engineering Conference (IECEC), Jul. 28-30, 2008, Cleveland, Ohio, published by the American Institute of Aeronautics and Astronautics, Inc.; the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a method and system for enhanced recovery of sulfur in a thermal stage process with simultaneous energy recovery and elimination of unwanted pollutants, such as sulfur dioxide. The controlled thermal stage causes the hydrogen sulfide to break up into sulfur dioxide which further reacts with hydrogen sulfide to form molten sulfur. The method and system result in much higher sulfur recovery in the thermal stage of the reactor than that possible in the thermal stage of currently used Claus process. The process can be used for the removal and clean conversion of any compound that decomposes in thermal environment and requires controlled thermo-chemical parameters for enhanced recovery and performance. 
     BACKGROUND 
     Sulfur-bearing compounds are very detrimental to the environment and to to industrial process equipment. They are often obtained or formed as a by-product of separation and thermal processing of fuels containing sulfur, such as coal, crude oil and natural gas. The two sulfur compounds, which need special attention, are: hydrogen sulfide (H 2 S) and sulfur dioxide (SO 2 ). H 2 S is a highly corrosive gas with a foul smell. 
     Hydrogen sulfide is present in numerous gaseous waste streams from natural gas plants, oil refineries, wastewater treatment, among other processes. These streams usually also contain carbon dioxide, water-vapor, trace quantities of hydrocarbons, sulfur and ammonia. Waste gases with ammonia are called sour gases, while those without ammonia are called acid gases. Sulfur must be recovered from these waste streams before flaring them. 
     SO 2  is a toxic gas responsible for acid rain formation and equipment corrosion. Various methods of reducing pollutants containing sulfur are described herein below, with a focus on the Claus process. The Claus process has been known and used in the industry for over 100 years. It involves thermal oxidation of hydrogen sulfide and its reaction with sulfur dioxide to form elemental sulfur and water vapor. The Claus process is equilibrium-limited and usually achieves efficiencies in the range of 94-97%, which have been regarded as acceptable in the past years. Nowadays strict air pollution regulations regarding hydrogen sulfide and sulfur dioxide emissions call for nearly 100% efficiency, which can only be achieved with process modifications. 
     Sulfur recovery from sour or acid gas typically involves application of the Claus process using the reaction between hydrogen sulfide and sulfur dioxide (produced in the Claus process furnace from the combustion of H 2 S with air and/or oxygen) yielding elemental sulfur and water vapor:
 
2H 2 S(g)+SO 2 (g) −&gt;(3 /n )S n (g)+2H 2 O(g)
 
with
 
ΔH r =−108 kJ moL −1  
 
     Therefore, higher conversions for this exothermic, equilibrium-limited reaction call for low temperatures which lead to low reaction rates, imposing the use of a catalyst. The catalytic conversion is usually carried out in a multi-stage fixed-bed adsorptive reactors process, to counteract the severe equilibrium limitations at high conversions. This technology process can possibly provide about 96-97% conversion of the influent sulfur in H 2 S to S. However, higher removal requires critical examination of the process and use of near isothermal reactor since the conversion is critically dependent upon exothermic and endothermic conditions of the reactions. Flameless combustion has been shown to provide uniform thermal field in the reactor so that the reactor temperature is near uniform. In addition it has been shown to result in compact size of the reactor, reduce combustion generated pollutants emission up to 50% and increase energy efficiency up to 30%. The application of this technology appears to offer great advantages for the process under consideration. 
     The adoption and further development of flameless combustion technology for sulfur recovery among other commercial and industrial heating processes is expected to be very crucial and beneficial, both economically and environmentally. 
     The conventional sulfur recovery process is based upon the withdrawal of sulfur by in-situ condensation within the reactor. The selective removal of water should, however, be a far more effective technique as its effect on the equilibrium composition in the mass action equation is much greater. The in-situ combination of the heterogeneously catalyzed Claus reaction and an adsorptive water separation seems especially promising, as both reaction and adsorption exhibit similar kinetics and pressure can be adapted to the needs of the adsorptive separation. Such an adsorptive reactor will lead to almost complete conversion as long as the adsorption capacity is not exhausted. There are numerous possibilities for implementing these two functionalities, ranging from fixed-beds with homogeneous catalyst/adsorbent mixtures to spatially structured distributions or even fluidized beds. 
     For the sulfur recovery process most of the previous studies have concentrated on the Claus catalytic conversion reactors and the Tail Gas Treatment Unit (TGTU). However, some previous studies have identified the Claus furnace as one of the most important yet least understood parts of the modified Claus process. The furnace is where the combustion reaction occurs with major initial sulfur conversion (through an endothermic gaseous reaction) takes place. Any SO 2  remaining is converted in the downstream catalytic stages. The contaminants (such as ammonia and BTX (benzene, toluene, xylene) are supposedly destroyed. The main two reactions in the Claus furnace are:
 
H 2 S+ 3/2O 2 →SO 2 +H 2 O  (1)
 
with
 
ΔH r =−518 kJ moL −1  
 
2H 2 S+SO 2 → 3/2S 2 +2H 2 O  (2)
 
with
 
ΔH r =+47 kJ moL −1  
 
     This last endothermic reaction is responsible for up to about 67% conversion of the sulfur at about 1200° C. Moreover, many side reactions take place in the furnace, which reduce sulfur recovery and/or produce unwanted components that end up as ambient pollutant emissions. Therefore, it would be useful to combine the endothermic and exothermic process using an isothermal reactor offered by the colorless (or flameless) oxidation combustion according to the present disclosure as described in the Detailed Description below. 
     A vast majority (about 92%) of the 8 million metric tons of sulfur produced in the United States in 2005 was recovered from industrial by-products using the Claus process. However, the traditional Claus process does face limitations and various process improvements have been investigated in order to satisfy the increasingly stringent emission regulations and the need to process gas streams and fuels with higher sulfur content. New technologies have to be developed in order to achieve near 100% removal of sulfur compounds from industrial flue gases. 
     A discussion follows regarding traditional sulfur recovery processes for understanding the Claus process. 
     The three main steps of sulfur recovery from sour gas are the following: 
     1. Amine Extraction: Gas containing H 2 S is passed through an absorber containing an amine solution (Monoethanolamine (MEA), Diethanolamine (DEA), Methyldiethanolamine (MDEA), Diisopropylamine (DIPA), or Diglycolamine (DGA)), where the hydrogen sulfide is absorbed along with carbon dioxide. A typical amine gas treating process includes an absorber unit and a regenerator unit as well as accessory equipment. In the absorber, the down-flowing amine solution absorbs H 2 S and CO 2  (referred to as acid gases) from the up-flowing sour gas to produce a sweetened gas stream (i.e., an H 2 S-free gas) as a product and an amine solution rich in the absorbed acid gases. The resultant “rich” amine is then routed into the regenerator (a stripper with a re-boiler) to produce regenerated or lean amine that is recycled for reuse in the absorber. The stripped overhead gas from the regenerator is concentrated H 2 S and CO 2 . The extracted mixture of H 2 S and CO 2 , referred to as an acid gas, is passed into the Claus unit for sulfur recovery. The process is also known as Gas sweetening and Acid gas removal. Amines are also used in many oil refineries to remove acid gases from liquid hydrocarbons such as Liquefied Petroleum Gas (LPG). 
     2. Claus Thermal Stage: H 2 S is partially oxidized with air (one-third of H 2 S is converted into SO 2 ) in the Claus furnace. The acid gas/air mixture is passed into a furnace operating at temperatures from 1300-1700 K, where the reactions are allowed sufficient time to reach equilibrium. The products from this step are: sulfur dioxide, water and unreacted hydrogen sulfide. Additionally some of the sulfur dioxide produced here reacts with hydrogen sulfide inside the furnace to produce sulfur according to reactions (1) and (2) shown above. The furnace products flow then into a waste heat boiler to condense the sulfur and produce high pressure steam for the Claus catalytic stages (see  FIG. 6 ). 
     Depending on the calorific value of the acid gas, various methods of stable burning are achieved. If very lean acid gases are involved (low calorific value) then auxiliary fuel, oxygen enrichment or a by-pass stream has to be used. The H 2 S-content and the concentration of other combustible components (hydrocarbons or ammonia) determine the location where the feed gas is burned. Claus gases (acid gas) with no further combustible contents apart from H 2 S are burned in lances surrounding a central muffle. Gases containing ammonia, such as the gas from the refinery&#39;s Sour Water Stripper (SWS) or hydrocarbons are converted in the burner muffle. 
     3. Claus Catalytic Stage: The remaining H 2 S, from the Claus furnace, is reacted with the SO 2  at lower temperatures (about 470-620 K) over an alumina- or titanium dioxide-based catalyst to make more sulfur:
 
2H 2 S+SO 2 →⅜S 8 +2H 2 O  (3)
 
ΔH r =−108 kJ moL −1  
 
     On average, about 70% of H 2 S and SO 2  will react via reaction (3). Note that in the catalytic stage mostly S 8  is produced, which is an exothermic reaction whereas in the thermal stage S 2  is the major product and the reaction is endothermic. Other allotropes of sulfur may also be present in smaller quantities. 
     The overall reaction for the entire process is:
 
3H 2 S+1.50 2 →3 /n S n +3H 2 O  (4)
 
ΔH r =−6268 kJ moL −1  
 
     Reactions (1) and (3) are exothermic and a cooling stage is needed following these steps in order to condense the sulfur produced. The condensed phase is then separated from the gas stream by draining it into a container. An interesting property of liquid sulfur is its increase in viscosity with temperature. This is due to polymerization of sulfur at around 430 K. Therefore, the temperature of condensed sulfur should be closely monitored to prevent polymerization and clogging of pipes used in the process. Care must also be taken in order not to pass condensed sulfur through the catalyst, which would become fouled and inefficient. Liquid sulfur adsorbs to the pores and deactivates the catalytic surface. Therefore, reheat stages using the previously generated steam are needed in order to keep the sulfur in gas phase while in the catalytic stage. Several methods of reheating used in industry are: 
     1. Hot-Gas Bypass: involves mixing the two process gas streams from the process gas cooler (cold gas) and the bypass (hot gas) from the first pass of the waste heat boiler. 
     2. Indirect Steam Reheaters: the gas can also be heated with high pressure steam in a heat exchanger. 
     3. Gas/Gas Exchangers: whereby the cooled gas from the process gas cooler is indirectly heated from the hot gas coming out of an upstream catalytic reactor in a gas-to-gas exchanger. 
     4. Direct-fired Heaters: fired reheaters utilizing acid gas or fuel gas, which is burned sub-stoichiometrically to avoid oxygen breakthrough and damage to Claus catalyst. 
     A typical Claus process involves one thermal stage followed by multiple catalytic stages in series to maximize efficiency. The need for multiple catalytic stages increases complexity and cost. Therefore, various methods of minimizing these steps in the process have been proposed. 
     A schematic of the process flow diagram along with approximate gas temperatures is shown in  FIG. 1 . The flow diagram includes a burner  10 , furnace  12 , boiler  14 , condensers  16   a ,  16   b , re-heater  18 , and catalytic stage  20 . During operation, high-pressure steam (40 atm) is generated in the boiler  14  and low-pressure steam (3-4 atm) is produced in the condensers  16   a  and  16   b . A total of two to four catalytic stages  20  are typically used in order to maximize efficiency. The tail gas  22  is either routed to a clean-up unit or to a thermal oxidizer to incinerate the remaining sulfur compounds into SO 2 . Where an incineration or tail-gas treatment unit (TGTU) is added downstream of the Claus plant, only two catalytic stages are usually installed. Before storage and downstream processing, liquid sulfur streams from the process gas cooler, the sulfur condensers and from the final sulfur separator are routed to the degassing unit, where the gases (primarily H 2 S) dissolved in the sulfur are removed. Over 2.6 tons of steam will be generated for each ton of sulfur yield. 
     The Claus process is equilibrium-limited. In the furnace stage the SO 2  produced from the combustion process (reaction 1) recombines with H 2 S in an endothermic reaction to form S 2  (reaction 2). Adequate residence time has to be provided in order to allow this reaction, responsible for 60-74% of sulfur conversion, to reach equilibrium. Since the main Claus reaction 3 is exothermic, this stage calls for the use of low temperatures in order to shift the equilibrium constant towards higher product yields. The low temperatures, however, lead to decreased reaction rates, hence the need for a catalyst. The law of mass action for the Claus reaction is as follows: 
     
       
         
           
             
               
                 
                   
                     
                       K 
                       p 
                     
                     ⁡ 
                     
                       ( 
                       T 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         p 
                         
                           
                             H 
                             2 
                           
                           ⁢ 
                           O 
                         
                         2 
                       
                       ⁢ 
                       
                         p 
                         
                           s 
                           8 
                         
                         
                           3 
                           / 
                           8 
                         
                       
                     
                     
                       
                         p 
                         
                           
                             H 
                             2 
                           
                           ⁢ 
                           S 
                         
                         2 
                       
                       ⁢ 
                       
                         p 
                         
                           SO 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Where, K P (T) is the chemical equilibrium constant and P H20 , P S8  are partial pressures of the products and P H2S &gt;P SO2  and partial pressures of the reactants. 
     This equation illustrates the nature of equilibrium limitations involved in the Claus process; decreasing the process temperature can increase the equilibrium constant and thus increase conversion, but the lower limit of this temperature and hence the upper is limit of equilibrium conversion is set by the condensation temperature of sulfur. A typical arrangement for the Claus sulfur recovery process is shown in  FIG. 2 . 
     Improvements on Claus Process: The traditional Claus process has been a reliable and relatively efficient way of removing hydrogen sulfide from the flue gas and converting it into elemental sulfur. It has, however, faced some shortcomings and limitations. Increasingly stringent air pollution regulations from oil, gas and chemical processing facilities combined with the fact that lower-grade, higher sulfur-content fuels will have to be used in the near future, call for improved efficiency of the process. 
     Eisner, et al. (M. P. Elsner, M. Menge, C. and Müller, D. W. Agar “The Claus Process: Teaching an Old Dog New Tricks” Catalysis Today 79-80 (2003) pp. 487-494) proposed an adsorptive water separation process applied in the catalytic reactor stage. Taking advantage of Le Chatelier&#39;s principle, this process removes H 2 O (one of the products) from the reaction, shifting equilibrium towards higher conversion (Equation (5)). An adsorptive reactor of this type could produce complete conversion in a single catalytic stage. 
     The Zeolite adsorbent beads saturate with water after a certain time and therefore need to be regenerated. This calls for a cyclic process where the flow of gas is reversed and hot gas is used to vaporize the adsorbed water off of the surface of Zeolite spheres and remove them from the reactor. The process can then be reversed again to regenerate the second adsorptive reactor ( FIG. 3 ). 
       FIG. 3  shows that 100% conversion can be achieved in the reactor for a longer time than in a conventional Claus reactor with no water adsorption. The decline in conversion efficiency after a period of about 1.3 hrs is due to the fact that the Zeolite spheres are saturated with steam and they need to be regenerated. It was also found that as a side effect of the water adsorption, the chemisorption of SO 2  on the surface of the alumina catalyst occurs. 
     A Cold Bed Adsorption (CBA) process, also known as the sub-dew point process developed by the Amoco Corporation has been shown to produce efficiencies in the range of 97.5-99.5%. In the CBA process the heterogeneous catalytic reaction is allowed to take place at low temperatures (below sulfur dew point), thus increasing equilibrium conversion. Additionally since the Claus reaction occurs in the gas phase, this liquid sulfur does not inhibit the reaction like sulfur vapor does, effectively removing one of the reaction products to result in a favorable shift in the reaction equilibrium and higher sulfur conversion. The condensed phase is then periodically desorbed from the catalytic surface by flowing hot gas through the unit to vaporize the condensate, thus regenerating the reactor. Therefore, this process is inherently a cyclic one. 
     There are normally two or more CBA reactors in series so that at least one can be operating sub-dew point while the other is being regenerated. Due to the cyclic nature of the CBA process, the CBA switching valves are subjected to very demanding sulfur vapor service that has caused significant operation and maintenance problems in many of the CBA plants. 
     Sulfur recoveries in excess of 99.5% have been achieved with the Modified Claus process with tail gas cleanup developed by Ortloff (“Modified Claus Process With Tail Gas Cleanup” http://www.ortloff.com/sulfur/claus-tailgas.htm). In this process the sulfur-bearing compounds (COS, CS 2 , SO 2 , SO 2 , S n ) in the tail gas are converted to H 2 S using hydrolysis and hydrogenation and recycled back into the Claus unit. Amine-based tail-gas cleanup is also used to recover the remaining hydrogen sulfide in the tail gas. 
     The Modified Claus Process with Tail Gas Cleanup Unit (TGCU) is used when very high sulfur recovery is necessary, such as for sulfur plants in petroleum refineries in the U.S. The U.S. EPA regulations normally require that the incinerated effluent from refinery sulfur plants contain no more than 250 ppmv SO 2  on a dry, oxygen-free basis. This usually corresponds to an overall sulfur recovery of 99.8-99.9%. The problem with any TGCU is that it usually costs as much as the whole Claus plant while it adds only about 2% in the total sulfur recovery. Lagas, et al. (J. A. Lagas, J. Borsboom, and G. Heijkoop “Claus Process Gets Extra Boost” Hydrocarbon Processing, April 1989: pp. 40-42) describe a selective oxidation process, in which the tail gas is selectively oxidized in the presence of active metal oxides to produce sulfur and small quantities of SO 2 . Total sulfur recovery of 99% has been achieved this way (99.4% with an additional hydrogenation step). 
     Oxygen enrichment technologies have been proposed to increase sulfur recovery, throughput of the system and decrease the size of the unit by reducing the amount of inert nitrogen from the process. The resultant high flame temperatures have to be dealt with using techniques such as staged combustion and water spraying because of material limitations. The increased complexity of the system is offset by the fact that better mixing, higher reaction rates, conversion and throughput for a given size of the unit are achieved. 
       FIG. 4  suggests that it is desirable to remove water from the reaction furnace during the process. As water is one of the products of the reaction, its removal will lead to the shift in equilibrium towards the product side and hence more conversion is achieved. 
     The removal of nitrogen and introduction of oxygen into the process has many effects. First, removal of the diluent nitrogen results in the increased partial pressure of each of the reacting species; second, the reduced volume of reacting gases is easier to mix; and, third, higher temperatures can be obtained. All three resulting in increases in the process rate ( FIG. 5 ). 
     The use of a gas recycling process has been proposed by the CNG group. The effluent gas from the first condenser was recycled back into the burner to attain overall sulfur recovery of 100%. However, intermediate stages had to be used to remove water vapor and nitrogen from the recycled gas to achieve efficient conversion and stable flame regime. A separator membrane can typically be used to separate nitrogen out of the stream. However, if pure oxygen is used in the combustion process, the membrane is not necessary and only water condensation is needed before the tail gas can be recycled back into the unit. 
     The heat recovery for this process is increased, since the water condensation heat can also be extracted out of the stream. In a recent work, El-Bishtawi, et al. (R. El-Bishtawi, and N. Haimour “Claus Recycle with Double Combustion Process” Fuel Processing Technology 86, pp. 245-260, 2004) describes a Claus recycle with double combustion process. The acid gas was partially combusted in the first furnace and the hot exhaust was passed into the second furnace where the remainder of oxygen was added to complete the reaction. The second furnace operated at a high temperature air combustion regime, since the inlet gas was above its auto-ignition temperature. 
     One sulfur condenser was used following the two furnaces. Part of the effluent gas was recycled back into the first furnace. It was reported that 100% conversion could be achieved without the use of catalytic reactors and with only one condenser. Such an arrangement should reduce the cost and complexity of the system by removing the catalytic stages. It was also found that the oxygen content should not exceed 78% in order not to exceed the maximum temperature limitations of the equipment materials. 
     SUMMARY 
     The present disclosure provides a method and system for recovering sulfur in a thermal stage process. In particular, the present disclosure relates to a method and system for enhanced recovery of sulfur in a thermal stage process with simultaneous energy recovery and elimination of unwanted pollutants, such as sulfur dioxide. The controlled thermal stage causes the hydrogen sulfide to break up into sulfur dioxide which further reacts with hydrogen sulfide to form molten sulfur. The method and system result in much higher sulfur recovery in the thermal stage of the reactor than that possible in the thermal stage of currently used Claus process. The process can be used for the removal and clean conversion of any compound that decomposes in thermal environment and requires controlled thermo-chemical parameters for enhanced recovery and performance. 
     The improved Claus process according to the present disclosure involves using high temperature air combustion technology (HiTAC) or otherwise called colorless (or flameless) combustion for application in Claus furnaces, especially those employing lean acid gas streams that contain large amounts of inert gas streams (such as nitrogen and CO 2 ) and which cannot be burned without the use of auxiliary fuel or oxygen enrichment under standard conditions. With the use of HiTAC, diluted H 2 S gas streams (less than 15% H 2 S), Low Calorific Value (LCV) fuels can be burned with very uniform thermal fields without the need for fuel enrichment or oxygen addition. The uniform temperature distribution favors clean and efficient burning with an additional advantage of significant reduction of NO x , CO and hydrocarbon emission. 
     The present disclosure further describes many different embodiments for a Claus reactor configured and designed for performing the improved Claus process according to the present disclosure. 
     These and other advantages and inventive concepts are described herein with reference to the drawings and the detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a flow diagram of a prior art Claus process; 
         FIG. 2  illustrates a prior art arrangement of a Claus unit; 
         FIG. 3  illustrates a graph of hydrogen sulfide conversion as a function of time; 
         FIG. 4  illustrates a graph of calculated hydrogen sulfide conversion as a function of reactor temperature for different oxygen concentrations; 
         FIG. 5  illustrates a graph of calculated concentrations of sulfur species as a function of temperature; 
         FIG. 6  illustrates a diagram of a Claus system with high temperature air combustion according to the present disclosure; 
         FIG. 7  illustrates a flameless Claus reactor having a flame zone that covers almost the entire area of the combustion chamber; 
         FIG. 8  illustrates a prior art Claus reactor having a flame zone that covers only a reduced area of the combustion chamber; 
         FIG. 9  illustrates an embodiment or configuration of a Claus reactor using HiTAC technology in accordance with the present disclosure; 
         FIGS. 10   a - 10   c  illustrate three different geometries for an interior of an input port of the Claus reactor taken along line A-A shown by  FIG. 9 ; and 
         FIGS. 11-23  illustrate additional embodiments or configurations of a Claus reactor using HiTAC technology in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Improvements on the Claus process in accordance with the present disclosure will now be described. In particular, a description is provided in Section I below directed to the use of HiTAC technology as a reliable and cost-effective alternative for improvement of concentrated or diluted acid gas treatment in the Claus process according to the present disclosure. The colorless or flameless (super-adiabatic) combustion according to the present disclosure is also described for processing acid-rich gas. Conclusions are presented in Section II. 
     I. Claus Process with HiTAC 
     In the case of diluted acid gas feeds (&lt;15% H 2 S) (or concentrated H 2 S gas streams) special considerations have to be taken in order to maintain a stable flame in the burner and achieve good combustion efficiency. Common approaches include: oxygen enrichment, a split-flow process and use of auxiliary fuel. In the case of oxygen enrichment the flame temperature is increased by removing part or all of inert nitrogen from air, thus decreasing the thermal loading of the system. In the split-flow process part of the acid gas is allowed to bypass the burner, which leaves adequate fuel/air proportions in the burner and higher flame temperature. The by-pass flow is then reintroduced into the furnace at a later stage in order to keep the H 2 S:SO 2  ratio 2:1 (Eq. 2 and 3) to maintain an overall equivalence ratio of 3. Change in the distribution of equivalence ratio in the combustion chamber can significantly reduce the efficiency. For example, at an equivalence ratio of 2, the sulfur capture efficiency is reduced to about 55%. With the use of auxiliary fuel the calorific value of the gas is increased. Stable flame of a higher temperature is therefore possible. 
     Paskall (Paskall H. G., 1979, Capability of the modified Claus process. Western Research, Alberta, Canada) collected a substantial amount of field data and reviewed the literature data on sulfur conversion in Claus furnaces and recommended that sulfur conversions are greater in furnaces that are designed for greater gas mixing and turbulence and equipped with burners that provide for good mixing of the feed gas and oxidizer and in furnaces of smaller volume. HiTAC or flameless or colorless combustion furnaces can achieve all of these recommendations and beyond, providing the highest sulfur recovery. Furthermore, Khudenko et al. (B. M. Khudenko, G. M. Gitman, and T. E. P. Wechsler “Oxygen Based Claus Process for Recovery of Sulfur from H 2 S Gases” Journal of Environmental Engineering, November/December 1993, pp. 1233-1251) through several thermodynamic and process simulation scenarios showed that a dual thermal stage system with cold products recycle (very similar to flameless concept) provides the greatest capacity reserve. They claimed that, with the dual stage system, no changes in the existing process train are required, even when the throughput capacity of the existing conventional system is more than doubled. 
     Economically this is very wise and attractive for increasing sour gas production in the oil and gas industry due to the exploitation of aging reservoirs. A reciprocal flow filtration combustor with embedded heat exchangers for super-adiabatic combustion has been proposed and studied by the Gas Technology Institute (GTI) and the University of Illinois at Chicago (Fabiano Contarin, William M. Barcellos, Alexi V. Saveliev, and A. Lawrence Kennedy, “Energy Extraction from a Porous Media Reciprocal Flow Burner With Embedded Heat Exchangers”, Journal of Heat Transfer, February 2005, Volume 127, Issue 2, pp. 123-130). The motion of the flame zone to the downstream of the reactant gas mixture results in positive enthalpy flux to the cold gas and thus increasing the reactant temperature prior to combustion. This is similar to the principles of HiTAC. 
     A prototype was build and tested for sulfur recovery at GTI. The results showed that the super-adiabatic combustion (which is very similar to flameless or colorless combustion in principle, but taking place in a non-catalytic porous medium) significantly extends conventional flammability limits to the region of the ultra-low heat content mixtures (such as lean acid gas) and features ultra low emissions for NO x  and CO. 
     Therefore, High Temperature Air Combustion (HiTAC) technology according to the present disclosure is an alternative treatment of lean to very diluted (&lt;15% H 2 S) Low Calorific Value (LCV) acid gases at very high sulfur recovery (about 74% in the thermal stage). This will reduce the number of expensive catalytic stages. While a stable conventional flame is usually not achievable in this regime, HiTAC provides very lean homogeneous thermal field uniformity flames. Moreover, uniform thermal characteristics with high and uniform heat flux distribution in the combustion chamber are achievable for high yield of sulfur with no release of sulfur dioxide to the environment. This results in high overall yield of sulfur (about 74% in the thermal stage) during the thermal stage conversion, low emissions of sulfur dioxide gas and other pollutants (such as oxides of nitrogen, carbon monoxide and black carbon) from the thermal process. 
     The process also reduces mechanical stresses associated with the more conventional high temperature combustion process that results in high temperature fluctuations and hot spot zones with maximum and minimum temperatures. Uniform thermal field in the process is especially useful to reduce NOx emissions by avoiding the “hot spots” zones in the flames that are responsible for thermal NOx formation and cause excessive noise. With the improved process the need for by-pass feed stream, oxygen enrichment and multiple furnaces can be eliminated as the lean acid gas could be oxidized in a single furnace operating above the auto-ignition temperature of the mixture, with good conversion efficiency. 
     In fact, it has been reported that HiTAC technology has shown significant reduction in pollutants emissions (about 50%), reduction in the size of the combustion chamber (about 25%), reduced thermal losses to the environment and significant energy savings (about 30%). High temperature air combustion is especially useful for reducing NO x  emissions due to its uniform thermal field and overall lower operating temperature and no adiabatic flame with hot spots that are responsible for thermal NO x  formation. With the use of HiTAC the need for by-pass feed stream, oxygen enrichment and multiple furnaces could be eliminated as the lean acid gas could be oxidized in a single furnace operating above the auto-ignition temperature, with good conversion. 
     As far as practical considerations are concerned, the Claus process is well suited for the use of HiTAC technology. A novel flameless Claus reactor using HiTAC technology in accordance with the present disclosure is shown by  FIG. 6  and designated generally by reference numeral  60 . As high pressure (HP) steam  62  is generated in a waste heat boiler  64  as well as in the condensers  66   a ,  66   b ,  66   c , it is readily available to preheat the incoming air stream  68  in a heat exchanger  70 . The incoming air stream  68  is heated in the heat exchanger  70  by the incoming high pressure steam  62  to generate hot air  72 . The hot air  72  is introduced, along with the acid gas  74 , to an efficient burner  76 . The burner  76  provides for good mixing of the feed gas  74  and oxidizer (hot air)  72 . Water  65  is used to cool the waste heat boiler  64 . 
     The byproducts of the burner  76  are then directed to a furnace  78  where the colorless (or flameless) oxidation combustion reaction and the initial sulfur conversion (through an endothermic gaseous reaction) take place and also where the SO 2  required by the downstream catalytic stages  80  is produced. The catalytic stages  80  produce low pressure steam  82  and tail gas  84 , as well as provide for the recovery of sulfur  86 . This Claus reactor is characterized as a flameless thermal Claus reactor since this controlled HiTAC condition provides an invisible flame in the thermal reactor. 
     As shown by the illustration of  FIG. 7 , the flameless Claus reactor  60  has a flame zone  40  that covers almost the entire area of the combustion chamber  42 . As a result, approximately all the sulfur-containing compounds  44  (i.e., H 2 S) entering the combustion chamber  42  via input port  46  are incinerated, thereby having a greater elemental sulfur and sulfur dioxide recovery yield than prior art Claus reactors. These substances exit or exhaust from the combustion chamber  42  via an exhaust/heat exchanger unit  48 . Unit  48  eliminates unwanted gases and also preheats the oxidizer before it is routed to input port  46 . 
     In contrast, in a prior art non-flameless Claus reactor (see  FIG. 8 ), the flame zone  50  covers only a reduced area of the combustion chamber  52 . As a result, not all of the sulfur-containing compounds  54  (i.e., H 2 S) which entered the reactor via input port  45  are incinerated. This is depicted by the H 2 S sulfur-containing compound  54  being outside the flame zone  50  in  FIG. 8 . This sulfur-containing compound  54  exits the reactor through an exhaust pipe  56 . 
     In High Temperature Air Combustion, the air is brought to above the auto-ignition temperature of the fuel to obtain uniform ignition and combustion characteristics across the reactor. The reported auto-ignition temperature of hydrogen sulfide (563 K or 290° C.) is lower than a typical auto-ignition temperature for hydrocarbon fuels (400-600° C.) and therefore requires less energy extraction from the high-pressure steam to achieve ignition and sustained combustion. During the transient start-up period, preheating with an electrical heater or auxiliary fuel can be used after which self-sustained operation at steady-state conditions can be maintained. Issues of air/fuel mixing, flame characteristics, such as temperature, size and flammability limits, that are relevant for the Claus process, must first be investigated. The resultant uniform thermal field in the flameless combustor plus gas recycling is expected to produce close to 100% conversion. 
     For rich acid gas oxidation, flammability limits and flame stability are not an issue due to the high calorific value of the gas. However, thermal field uniformity offered by flameless or colorless combustion would always promote better conversion and lower pollutant emissions, among other benefits as mentioned above. Furthermore the super-adiabatic flame studies, discussed earlier, featured that fuel rich (much more than stoichiometric H 2 S to oxygen ratio) conditions promote H 2 S conversion to H 2  and S 2  rather than H 2 O and SO 2 . Their numerical results showed that at a super-adiabatic temperature of about 1650K and an equivalence ratio of about 10, an overall H 2 S conversion of 50% resulted with an H 2 /H 2 O selectivity of 57/43 and an S 2 /SO 2  selectivity of 99/1. These conditions, with even higher temperature, would be easily attained under flameless combustion with H 2 S recycling and pre-heating. This flameless combustion assisted-thermal decomposition of H 2 S would then eliminate any catalytic stage use and produce hydrogen which is highly needed in fuel processing and power production. 
     The thermal decomposition of H 2 S is a well researched route for the production of hydrogen and Cox et al. (Cox B. G., Clarke P. F. and Pruden B. B., 1998, Economics of thermal dissociations of H 2 S to produce hydrogen, Int. J. Hydrogen Energy, Vol. 23, No. 7, pp. 531-544) presented a study on the economics of thermal dissociation of H 2 S to produce hydrogen and some studies are even at the pilot plant stage. However, none of the early studies address the problem of heat transfer. Due to the endothermic heat of reaction, heat transfer limits the overall rate of reaction resulting in low conversions. However, with flameless or colorless combustion the H 2 S rich mixture reacts in a very hot homogeneous medium with no heat transfer limitations and therefore will present much higher conversions. 
     A description will now be provided with reference to FIGS.  9  and  11 - 23  which illustrate different embodiments or configurations of a flameless Claus reactor using HiTAC technology in accordance with the present disclosure. It is contemplated that these embodiments can be used for other chemical reactions besides performing the chemical reactions (1) and (2) associated with a Claus reactor. In each embodiment, the exhaust port also includes a heat exchanger for pre-heating the oxidizer before it is routed to one or more input ports. 
       FIG. 9  illustrates an embodiment of a Claus reactor  90  having four input ports  92   a - d  for introducing a mixture of hydrogen sulfide and a preheated oxidizer  94  within a combustion chamber  96  of the reactor  90 . The oxidizer is heated by directing it in close proximity to a heat exchanger  98  which absorbs heat exiting from the exhaust  100 . The preheated oxidizer  94  and the hydrogen sulfide gas chemically react forming an H 2 S/oxidizer flamelet  102  for each input port  92 . The flamelets  102  incinerate the hydrogen sulfide gas within a uniform thermal (flameless) combustion zone  104 . 
     The Claus reactor  90  enables the combustion of hydrogen sulfide while simultaneously recovering sulfur and thermal energy at higher efficiency than prior art Claus reactors. 
       FIGS. 10   a - 10   c  illustrate three different geometries for an interior  106  of the input ports  92   a - d  of the Claus reactor  90  taken along line shown by  FIG. 9 . The geometry of the input port  92  determines the direction(s) of the internal flow pattern  106  as shown by  FIGS. 10   a - 10   c . Other factors that can be used to affect the direction(s) of the internal flow pattern is the location of an input port(s) for introducing an oxidizer fluid with respect to the location of an input port(s) for introducing hydrogen sulfide (see, e.g.,  FIGS. 11-18 ); velocity of the fluids introduced into the combustion chamber  96 ; the combustibility of the fluids; temperature within the combustion chamber  96 ; premixing the hydrogen sulfide with other fluids, such as nitrogen and/or carbon dioxide; and by controlling the amount of oxidizer introduced into the combustion chamber  96  via an air introduction system. 
     The reactor  90  and the other novel reactors described herein with respect to  FIGS. 6 ,  7  and  11 - 23  include one or more control modules  97  for controlling one or more of these factors which in turn controls the internal flow pattern, mixing and thermal field uniformity, and hence the amount of sulfur recovered and the amount of thermal energy. For example, it is desired for the temperature within the combustion chamber  96  to be less than 25K for optimum sulfur recovery. 
       FIG. 10   a  illustrates the input port  92  having two side ports  110   a  and  110   b  for directing hydrogen sulfide gas to the combustion chamber  96 , and one, unobstructed main port  110   c  for directing a preheated oxidizer to the combustion chamber  96  for mixing with and reacting with the hydrogen sulfide gas. The hydrogen sulfide gas and the preheated oxidizer are injected perpendicular to each other forming an internal flow pattern  106  in one direction. 
     The internal flow pattern  106  in the configurations shown by  FIGS. 10-10   c , as well as  FIGS. 11-18 , operates as an induced jet pump which causes significant recirculation of the oxidizer prior to chemical reaction of the reactants. This recirculation of the reactants maximizes the amount of sulfur recovered. The internal flow pattern can include swirl motion  108  ( FIGS. 10   b  and  10   c ) by obstructing the main port  100   c  with a divergent conical body  112  ( FIG. 10   b ) or a convergent conical body  114  ( FIG. 10   c ). The swirl motion  108  produces desired thermal characteristics within the reactor  90 , such as a uniform and defined thermal set point, and an increase in the amount of thermal energy generated. The internal flow pattern can also include other types of motion, including spiral motion as shown by  FIGS. 11-18 . 
       FIG. 11  illustrates an embodiment of a Claus reactor  200  having two separate input ports  202 ,  204  on the same side of the reactor  200 . One input port  202  is used for introducing an oxidizer into a combustion chamber  206 . The other input port  204  is used for introducing hydrogen sulfide into the Claus reactor  200 . The two reactant fluids intermix at an opposite end  208  of the reactor  200  forming a uniform thermal distribution flow pattern  210 . The pattern  210  is formed in a central area of the combustion chamber  206  as shown by  FIG. 11 . An output port  212  is provided for the exhaust fluids to exit or exhaust from the combustion chamber  206 . 
       FIG. 12  illustrates an embodiment of a Claus reactor  300  similar to the embodiment shown by  FIG. 11 . The Claus reactor  300  has two separate input ports  302 ,  304  on the same side of the reactor  300 . One input port  302  is used for introducing a hydrogen sulfide-oxidizer mixture into a combustion chamber  306 . The other input port  304  is used for also introducing a hydrogen sulfide-oxidizer mixture into the Claus reactor  300 . The hydrogen sulfide and the oxidizer are premixed. The two reactant fluids intermix at an opposite end  308  of the reactor  300  forming a uniform thermal distribution flow pattern  310 . The pattern  310  occupies almost entirely the interior area of the combustion chamber  306  as shown by  FIG. 12 . An output port  312  is provided for the exhaust fluids to exit the combustion chamber  306 . 
       FIG. 13  illustrates an embodiment of a Claus reactor  300  designated by reference numeral  400 . The Claus reactor  400  has a plurality of input ports  402  located on three sides of the reactor  400 . Each input port  402  is used for introducing a hydrogen sulfide-oxidizer mixture into a combustion chamber  406 . The hydrogen sulfide and the oxidizer are premixed. The two reactant fluids intermix within the combustion chamber  406  forming a uniform thermal distribution flow pattern  410 . The pattern  410  occupies almost entirely the interior area of the combustion chamber  406  as shown by  FIG. 13 . An output port  412  is provided for the exhaust fluids to exit the combustion chamber  406 . 
       FIG. 14  illustrates an embodiment of a Claus reactor  500  similar to the embodiments shown by  FIGS. 11 and 12 . The Claus reactor  500  has two separate input ports  502 ,  504  on the same side of the reactor  500 . One input port  502  is used for introducing an oxidizer into a combustion chamber  506 . The other input port  504  is used for introducing hydrogen sulfide into the Claus reactor  500 . The two reactant fluids intermix in a central area of the reactor  500  forming a uniform thermal distribution flow pattern  510 . The pattern  510  occupies a central area of the combustion chamber  506  as shown by  FIG. 14 . An output port  512  is provided for the exhaust fluids to exit the combustion chamber  506 . The flow pattern  510  is facilitated by the positioning of two triangular bodies  514  in proximity to the output port  512 . A side of each triangular body  514  elongates the length of the output port  512  to an area within the combustion chamber  506  so that the H 2 S gas stream is not directed with the exhaust fluids to the output port  512 . 
       FIG. 15  illustrates an embodiment of a Claus reactor  600  having two separate input ports  602 ,  604  on the same side of the reactor  600  for introducing hydrogen sulfide into a combustion chamber  606 . The reactor  600  also includes two separate input ports  614 ,  616  on an opposite side from the input ports  602 ,  604  for introducing an oxidizer into the combustion chamber  606 . The reactant fluids intermix throughout a central area of the reactor  600  forming a uniform thermal distribution flow pattern  610 . The pattern  610  is formed in the central area of the combustion chamber  606  as shown by  FIG. 15 . Two output ports  612  are provided on opposite ends of the reactor  600  for the exhaust fluids to exit the combustion chamber  606 . 
       FIG. 16  illustrates an embodiment of a Claus reactor  700  having two separate input ports  702 ,  704  on the same side of the reactor  700  and positioned at an angle of approximately 45 degrees from a horizontal axis of the reactor  700 . One input port  702  is used for introducing an oxidizer into a combustion chamber  706 . The other input port  704  is used for introducing hydrogen sulfide into the Claus reactor  700 . The two reactant fluids intermix at a central area of the combustion chamber  706  forming a uniform thermal distribution flow pattern  710 . The pattern  710  is formed in a central area of the combustion chamber  706  as shown by  FIG. 16 . An output port  712  is provided for the exhaust fluids to exit the combustion chamber  706  at an end opposite the end where the input ports  702 ,  704  are located. 
       FIG. 17  illustrates an embodiment of a Claus reactor  800  having three separate input ports  802 ,  804 ,  808 . Two of the input ports  802 ,  804  are located on two different sides opposite from each other, and one input port  808  is located at a third side. The input port  808  is used for introducing an oxidizer into a combustion chamber  806 . The other input ports  802 ,  804  are used for introducing hydrogen sulfide into the Claus reactor  800 . The two reactant fluids intermix towards the right region of the reactor  800  forming a uniform thermal distribution flow pattern  810  as shown by  FIG. 17 . An output port  812  is provided for the exhaust fluids to exit the combustion chamber  806 . It is contemplated that obstructing bodies are placed in proximity to the input ports  802 ,  804  within the combustion chamber  806  for obstructing the flow of the incoming fluids and force them to be directed towards a desired direction and/or create an incoming flow pattern. 
       FIG. 18  illustrates an embodiment of a Claus reactor  900  having two separate input ports  902 ,  904  on opposite sides of the reactor  900 . One input port  902  is used for introducing an oxidizer into a combustion chamber  906  from a top-left area of the combustion chamber  906 . The other input port  904  is used for introducing hydrogen sulfide into the Claus reactor  900  from a bottom-right area of the combustion chamber  906 . The two reactant fluids intermix forming a uniform thermal distribution flow pattern  910 . The pattern  910  is formed in a central to high region of the combustion chamber  906  as shown by  FIG. 18 . An output port  912  is provided for the exhaust fluids to exit the combustion chamber  906 . A separating wall  914  is also included to separate the area of the combustion chamber  906  where intermixing between the reactants occurs and an area of the combustion chamber  906  where no intermixing occurs. Obstructing bodies  916  are placed within the combustion chamber  906  so that the H 2 S gas stream is not directed with the exhaust fluids to the output port  912 . 
       FIG. 19  illustrates an embodiment of a Claus reactor  1000  similar to the embodiment shown by  FIG. 14 . The Claus reactor  1000  includes two separate input ports  1002 ,  1004  located on the same side of the Claus reactor  1000 . One input port  1002  is used for introducing an oxidizer into a combustion chamber  1006 . The other input port  1004  is used for introducing hydrogen sulfide into the combustion chamber  1006 . The two reactant fluids intermix in a central area of the reactor  1000  forming a uniform thermal distribution flow pattern  1010 . The pattern  1010  occupies a central area of the combustion chamber  1006  as shown by  FIG. 19 . An output port  1012  is provided for the exhaust fluids to exit the combustion chamber  1006 . The flow pattern  1010  is facilitated by the positioning of two concave bodies  1014  in proximity to the output port  1012 . A side of each concave body  1014  elongates the length of the output port  1012  to an area within the combustion chamber  1006  and also causes the oxidizer and the hydrogen sulfide to be directed towards the input ports  1002 ,  1004 . 
       FIG. 20  illustrates an embodiment of a Claus reactor  1100  having seven separate input ports  1002   a - d ,  1004   a - c  located on two different sides of the Claus reactor  1100 . Input ports  1002   a - d  are used for introducing an oxidizer into a combustion chamber  1106 . The other input ports  1004   a - c  are used for introducing hydrogen sulfide into the combustion chamber  1106 . The two reactant fluids intermix in a central area of the reactor  1100  forming a uniform thermal distribution flow pattern  1110 . The pattern  1110  occupies a central area of the combustion chamber  1106  as shown by  FIG. 20 . Two output ports  1012   a - b  are provided for the exhaust fluids to exit the combustion chamber  1106 . 
       FIG. 21  illustrates an embodiment of a Claus reactor  1200  having four separate input ports  1202   a - d  located on one side of the Claus reactor  1200  for introducing an oxidizer into a combustion chamber  1206 . There is also one other input port  1204  located on an opposite side of the Claus reactor  1200  for introducing hydrogen sulfide into the combustion chamber  1206  via six sub-input ports  1206 . The two reactant fluids intermix in a central area of the reactor  1200  forming two uniform thermal distribution flow patterns  1210   a - b . The patterns  1210   a - b  occupy a top and bottom central area of the combustion chamber  1206  as shown by  FIG. 21 . Two output ports  1212   a - b  are provided for the exhaust fluids to exit the combustion chamber  1206 . 
       FIG. 22  illustrates an embodiment of a Claus reactor  1300  having three separate input ports  1302   a - c  located on one side of the Claus reactor  1300  for introducing an oxidizer into a combustion chamber  1306 . There is also one other input port  1304  located on a side perpendicular to the one side of the Claus reactor  1300  for introducing hydrogen sulfide into the combustion chamber  1306  via six sub-input ports  1306 . The two reactant fluids intermix in a central area of the reactor  1300  forming a uniform thermal distribution flow pattern  1310 . The pattern  1300  occupies a central area of the combustion chamber  1306  as shown by  FIG. 22 . Two output ports  1312   a - b  are provided for the exhaust fluids to exit the combustion chamber  1306 . 
       FIG. 23  illustrates an embodiment of a Claus reactor  1400  having three separate input ports  1402 ,  1404   a - b  located on one side of the Claus reactor  1400  for introducing an oxidizer into a combustion chamber  1406  via input port  1402  and hydrogen sulfide via input ports  1404   a - b . There are twelve sub-input ports  1408  for input port  1402  and six sub-input ports  1409  for each of input port  1404   a - b . The two reactant fluids intermix in a central area of the reactor  1400  forming a uniform thermal distribution flow pattern  1410 . The pattern  1400  occupies a central area of the combustion chamber  1406  as shown by  FIG. 23 . Two output ports  1412   a - b  are provided on opposite sides from each other for the exhaust fluids to exit the combustion chamber  1406 . 
     It can be seen from the embodiments described above that the uniform thermal distribution flow patterns can be formed based on the number of input ports for the oxidizer and for the hydrogen sulfide, and/or the interior design of the combustion chamber. Accordingly, the uniform thermal distribution flow pattern(s) for a Claus reactor according to the present disclosure can be controlled based on the design of the flameless Claus reactor. 
     II. Conclusions 
     A new sulfur recovery process from acid gases is described above and claimed below that provides much higher efficiency than the more commonly used Claus flame thermal reactor. The conventional and modified Claus process and its derivatives have been presented and discussed, each with distinct advantages. It is shown that any improvements towards high sulfur recovery cause very high cost additions to an already economically deficient process. 
     The Claus reactor according to the present disclosure features greater yield of sulfur and chemical energy without any environmental impact. The lean acid gases provide complete sulfur recovery from more conventional stream while controlled well mixed advanced Claus reactor provides high yield of sulfur recovery under conditions of fuel-rich acid gas composition. Therefore, the technology according to the present disclosure features a new way for the efficient low cost removal of chemically bound sulfur in the gas to sulfur and chemical energy, thus reducing the complexity and the cost of the more traditional Claus sulfur recovery process. 
     The described embodiments of the present disclosure are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present disclosure. Various modifications and variations can be made without departing from the spirit or scope of the disclosure as set forth in the following claims both literally and in equivalents recognized in law.