1、BTEX Prediction & Removal in Amine Units,Luke Burton Chad Duncan Armando Diaz Miguel Bagajewicz,Project Objective,To study means of reducing incineration expenditures associated to BTEX capture in Amine units, through Process parameter optimization Alternative/Additional Technologies to capture BTEX
2、 Specifics: BTEX content of needs to be kept under the EPA emission limit of 25 Ton/year . If this is achieved, a reduction in incineration temperature from 1500 oF to 1350 oF can be accomplished with an associated savings of $303 Thousand. Alternative Technologies, if they exist, ought to have a lo
3、wer cost.,Project Methodology,Discuss Existing Simulators and compare their capabilities of predicting Acid Gas flowrate and composition BTEX capture Determine ways of using these simulators to make approximate predictions Assess the ability of process parameter manipulation to achieve the reduction
4、 of BTEX capture goal. Study Alternative Technologies Adsorbents Ionic Liquids,Modeling Objective,Commercial Simulators seem not to reproduce reliable results in the case of Amine units, especially when BTEX capture is of interest. Ideal Objective: Have a simulator that will use the right thermodyna
5、mic equation of state and liquid activity coefficientsAchievable Objectives: Use existing simulators and supersede them with additional data and make conclusions.,Amine Plant at Glance,BTEX Problems in Amine Unit,Flash Drum BTEX is emitted to the atmosphere, possible violating EPA guidelines.Acid ga
6、s stream BTEX present has to be incinerated at high temperatures, therefore incurring a high fuel cost.Sweet gas stream Some BTEX will be present, so it is removed in glycol unit.,PRO II Amine Unit Simulation,Same inlet conditions were used: Feed gas (575MMSCF), T (85F), P (500psia), same compositio
7、ns.Results were compared to 92 wt% of CO2 usually found in acid gas stream.,AmineCalc Amine Unit Simulation,Same inlet conditions were used: Feed gas (575MMSCF), T (85F), P (500psia), same compositions.Results were compared to 92 wt% of CO2 usually found in acid gas stream.,CO2 Results from Pro II a
8、nd AmineCalc,Credibility,Which simulator is correct? AmineCalc renders 99 wt% of CO2 in the acid gas Pro II renders 94 wt% of CO2 in the acid gas, closer to the 92 wt % reported from field data. Thermodynamic packages in AmineCalc and Pro II might explain why.,EOS in AmineCalc,Uses Peng-Robinson equ
9、ation of state.Not as thorough as Pro II as far as the thermodynamics. Binary interaction coefficient calculated by using simple cubic mixing rule. Mixing rule have been shown to be incapable of modeling real systems.,EOS in Pro II,Pro II uses SRKM equation of state to calculate the vapor phase enth
10、alpy and density, and liquid and vapor phase entropy. , cij, kij, b, are parameters that are easily obtained. Binary interaction coefficients mixing rule developed by Prausnitz, and shown to perform better than simple cubic mixing rule.,BTEX Predictions,USE OF EXTERNAL DATA,We used the solubility da
11、ta found in Developments and Applications in Solubility. (Coquelet et. al. 2007)In this book, the activity coefficients of benzene, toluene, ethylbenzene, and xylene are calculated experimentally for different mixtures of MDEA/DGA and Water.,Contactor Tower Results,Experimental results can be used t
12、o calculate how accurate are the simulator results; more specifically the molar composition in the liquid stream.,Contactor Tower,Sweet Gas,Amine,Contactor Tower Results,G,L2,L1,V,Contactor Tower Results,Regenerator Tower Results,Experimental results can be used to calculate how accurate are the sim
13、ulator results; more specifically the molar composition in the acid gas stream.,Regenerator Tower,Acid Gas,Vapor tray 3,Liquid tray 2,Rich Amine,Lean Amine,RESULTS,CONCLUSION,It is our belief that Pro II produces good answers for flows and CO2 concentrations in the amine unit. Pro II and AmineCalc o
14、verestimates the solubility of BTEX in the contactor. We do not have the right thermodynamics in Pro II or AmineCalc, or any simulator. Despite the above, we have a credible way of estimating solubilities based on experimental data.,Glycol Dehydration Units,Unit removes water from sweetened natural
15、gas. Glycols such as DEG or TEG usually used for these tasks. Two commercially available simulators: GlyCalc and Pro II. Interfaces for Glycalc and Pro II are shown.,Glycol Dehydration Units,Unit removes water from sweetened natural gas. Glycols such as DEG or TEG usually used for these tasks. Two c
16、ommercially available simulators: GlyCalc and Pro II. Interfaces for Glycalc and Pro II are shown.,Milagro Data: 49 MMSCFD 104 F 887 psig 10gal/min glycol 382 F,GlyCalc Contactor Tower,In contactor tower, VLE calculations using Kremser-Brown approximation. Approximation used to calculate K-values. C
17、ontactor tower not rigorously modeled by using stage by stage flash calculation. L and V is assumed to be average in every stage.,GlyCalc Regenerator,For regenerator, manual notes: “to avoid complex heat and material balances that would be needed if the regenerator were rigorously modeled, a simple
18、empirical calculation is used”,Results,Conclusions,GlyCalc produces better results for BTEX in dehydration unit.We believe Glycalc would be able to predict the amount of BTEX present in dehydration unit.GlyCalc would not be able to accurately predict duty in regenerator due to its simple correlation
19、 used for energy balance.,BTEX Solutions,Reduction Possibilities,Two different ways to remove amine existReduce absorption in amines Certain parameters can obtain thisRemove BTEX prior/post amine unit treating Solvent Alternative Technologies,First Solution,Changes in parameters such as amine flow r
20、ate, temperature and pressure of towers, etc. may reduce BTEX capture.We performed a few simulations in Pro II to get a preliminary sensitivity analysis for the affect of temperature.,Parameter Adjustments,It is our belief that this route will not solve the emission problems.,Second Solution,Solvent
21、s can be used: WaterAlternative Technology Adsorbents Activated Carbon Silica Aerogels Macroreticular Resins Ionic Liquids,Removal by Solvent,Removal By Water,CONCLUSION,Manipulating the amine unit parameters (T, P, and flow rates) will not lead to the order of magnitude changes needed to reduce the
22、 emission. This conclusion is based both on considering results of Pro II directly and calculations based on experimental results. Water is also not a good solvent to remove BTEX due to separation complications. This leads to the investigation of other alternative technologies,Activate Carbon,Activa
23、ted Carbon has a density of about 350 kg/m3 and surface area of 500 m2/gCan only be used 2 cycles before 50% adsorption reduction occurs,Macroreticular Resins,Macroreticular resins have an adsorption of BTEX of about: 350 mg BTEX/1000 mg of adsorbent *(Lin (1999)Can adsorb and desorb BTEX for 42 cyc
24、les before a 10% reduction in adsorption,Silica Aerogels (SAG),Hydrophobic material that has low density (0.3-0.05 g/cm3), high porosity, and high surface area (500- 1000 m2/g).,SA can be used up to 14 cycles!,Incineration Results,From Pro/II, it was calculated how much fuel gas (methane) will be ne
25、eded to fully incinerate the acid gas stream at 1500F by using a Gibbs reactor. These calculations were based from on the following field data:,Flame Temperature Verification,We took initial and final moles from Pro II. Reaction was carried while keeping the vent gas temperature at 1500F. Pro II res
26、ults agreed with field data within 1.3% margin of error. Pro II results agreed with hand calculations within .64% margin of error.,Excess Air Limits,The Limit of excess is such that the mole percent of oxygen released to the atmosphere must be between 1-3% (Lewandowski, 2000). Lower limit due to for
27、mation of CO below 1% O2 Upper limit exist to reduce formation of NOx which occur above 3% oxygenThis data is backed by Ignacio plant data with O2 level of 2% in outlet stream,Flame Temperature VOC,The flame of incinerator must be risen to a temperature, Auto Ignition Temperature, high enough to com
28、bust VOCs:In order to incinerate at this temperature, long residence times in incinerator must be used A common rule of thumb for 99% incineration efficiency at .5 seconds is to add 400F onto AIT.,* (Lewandowski, 2000).,Fuel Cost,*Cost of Methane at $5/MMBtu*,SAG Adsorption Process,One tank opened w
29、hile the other is closed, and they will run for 12 hr periods. From the columns, the BTEX can be removed by using three different designs. These columns could be used up front of amine unit or in Acid Gas.,Acid Gas/Raw Gas,Comparison of Two Designs,Removing the BTEX present in the columns by blowing
30、 air through the columns.,Instead of burning the air/BTEX stream, run the stream through a condenser, and then pass it through a flash.,Activated Carbon Acid Gas,Activated Carbon cost $4 per kg. Used Pro-II Results from Milagro Type Plant This design would have an additional cost of $191,000 In orde
31、r for a saving of $100,000 to be reached price would have to be reduced to $1.15 per kg 71% discount needed,Silica Aerogels Acid Gas,Silica Aerogels cost $37 per kg from Cabot. Used Pro-II Results from Milagro Type Plant This design would produce a savings of $76,000 In order for a saving of $100,00
32、0 to be reached price would have to be reduced to $34 per kg 8% discount needed,Macroreticular Resins Acid Gas,Macroreticular resins cost $43 per kg from Dow Chemical. Used Pro-II Results from Milagro Type Plant This design would produce a savings of $61,000 In order for a saving of $100,000 to be r
33、eached price would have to be reduced to $35 per kg 19% discount needed,Conclusions from Adsorption,There exist a saving of $303,000 in reducing the flame temperature from 1500F to 1350F.This savings can then be used to design adsorption columns to remove BTEX. Out of all the adsorbents studied sili
34、ca aerogels proved to be the best adsorbent on the basis of savings and reduced cost.,Ionic Liquid Background,Ionic liquids can be used to remove carbon dioxide.The expense of using these liquids will be examined in comparison with that of the amine unit.,Amine Unit Cost,Ionic Liquid Conclusion,Ionic Liquid Conclusion,QUESTIONS?,
