1. Heat-Integrated Distillation Column* Stephanie N. English**, Su Zhu**, and Miguel J. Bagajewicz University of Oklahoma - Chemical Engineering (*) This work was done as part of the capstone Chemical Engineering class at the University of Oklahoma (**) Capstone Undergraduate Students Abstract We apply the concept of Heat-integrated Distillation Column (HIDC) to crude fractionation. HIDC columns save energy by recovering excess heat from the rectifying section for usage in the stripping section. We show the new column design and present the results. We found our version of HIDC applied to crude fractionation to be less profitable than the conventional method. In the process of developing the HIDC, two alternative methods for distillation operation were invented. These alternative methods have shown profit potential compared to the conventional method. - - Methods and Costs II. Energy Integration and Performance Improvement Potential I. Process Flow Diagrams References Acknowledgements Summary III. Crude Columns With HIDC Concepts IV. HIDC with Additional Trays V. New Technology: Method 1 VI. New Technology: Method 2 A: Conventional crude distillation A B C A A DuyQuang Nguyen 1.Iwaskabe, K.; Nakaiwa, M.; Huang, K.; Nakanishi, T.; Rosjorde, A.; Ohmori, T.; Endo, A.; Yamamoto, T. Energy Saving in Multicomponent Separation Using an Internally Heat-Integrated Distillation Column (HIDiC). Applied Thermal Engineering. 2006, 26, 1362. 2.Iwaskabe, K.; Nakaiwa, M.; Huang, K.; Nakanishi, T.; Rosjorde, A.; Ohmori, T.; Endo, A.; Yamamoto, T. Performance of an Internally Heat-Integrated Distillation Column (HIDiC) in Separation of Ternary Mixtures. Unpublished. 3.Iwaskabe, K.; Nakaiwa, M.; Huang, K.; Nakanishi, T.; Ohmori, T.; Endo, A.; Yamamoto, T. Recent Advances in the Internally Heat-Integrated Distillation Columns (HIDiC). Unpublished. 4.Sharma, R.; Jindal, A.; Mandawala, D.; Jana, S. Design/Retrofit Targets of Pump-Around Refluxes for Better Energy Integration of a Crude Distillation Column. Ind. Eng. Chem Res. 1999, 38, 2411. 5.Bagajewicz, M.; Ji, S. Rigorous Procedure for the Design of Conventional Atmospheric Crude Fractionation Units. Part I:Targeting. Ind. Eng. Chem. Res. 2001, 40, 617. 6.Olujic, Z.; Fakhri, F.; de Rijke, A.; de Graauw, J.; Jansens, P. Internal Heat Interation-The Key to an Energy-Conserving Distillation Column. J. Chem. Technol. Biotechnol. 2003, 78, 241. 7.Engelien, H.K.; Larsson, T.; Skogestad, S. Implementation of Optimal Operation for Heat Integrated Distillation Columns. IChemE. 2003, 81 (A), 277. 8.Nakaiwa, M.; Huang, K.; Owa, M.; Akiya, T.; Nakane, T.; Sao, M. Characteristics of Energy Savings in an Ideal Heat-Integrated Distillation Column (HIDiC). 1587. Columns process 120 Mbbl of 36.0 API crude oil per day as basis for comparison All simulations were run in SimSci-Esscor Pro/II as a continuous fractionation process The performance of four columns was compared to the conventional system –Heat-Integrated Distillation Column 2:1 compression ratio, heat transferred from tray 28 to tray 33 Furnace temperature reduced by duty equal to heat integrated –Heat-Integrated Distillation Column (increased stripping trays) 2:1 compression ratio, heat transferred from tray 28 to tray 49 Furnace temperature reduced by duty equal to heat integrated –New Methods 1 and 2 Novel ideas currently under Oklahoma Technology Development consideration 1.By increasing the pressure of the rectifying section of a conventional crude fractionation system, certain trays in the rectifying section will have a higher temperature than trays in the stripping section. This allows for heat to be transferred from the stripping section to heat the rectifying section. However, separation efficiency decreases and more components end up in the residue. This process seems to be less profitable. This modification to crude fractionation is unreasonable under the conditions studied. 2. By adding additional trays to the rectifying section of the column, the total utility needed to fractionate crude decreases. However, this results in a decrease in production of gasoil. Again, this modification would be undesirable at current market conditions. This modification to crude fractionation is also unreasonable under the conditions studied. 3. Two novel concepts for crude fractionation were developed. One simulations shows that it can significantly increase the amount of high- value components produced during crude fractionation. The other simulation uses significantly less energy to fractionate crude. Overall, both processes show potential of being more profitable. Costs Total Cost Differential= (U conv – U new )*Cost heat + (C conv -C new )*Cost cooling Product Profit Differential= Naphtha: $110/bblKerosene: $95/bbl Diesel: $109.9/bblGasoil: $75.9/bbl Residue: $67.9/bbl U total -total utility required, U hot -heating utility, H i s - steam enthalpy, W-compressor work, C-cooling utility, i-flowrate of product Key Variable - heat Valve A) The conventional method of crude distillation. Consists of 34 trays at atmospheric pressure and side heaters with 6 trays each. The pre-heated feed enters at tray 29. B) Basic heat-integrated distillation column. Features a high-pressure stripping section that sends heat to the stripping section. C) The developed heat-integrated distillation column for crude fractionation. This is the basic design of all columns in this study. A)The vapor flowrate profile of the conventional distillation column. Since there is no reboiler, very little vapor is in the stripping section. The blue line represents the location of pre-heated feed, while the red lines show where the pump-arounds return the cooled liquid into the column. Additional heat in the stripping section can increase the separation efficiency of the column and save overall utility. B) Temperature profile near the feed tray (red line). The conventional column has no trays in the rectifying section are at a higher temperature than the stripping section. To have a temperature driving force, the pressure in the rectifying section has to be increased. The HIDC has potential for heat exchange due to the temperature driving force of the rectifying section.. A A) Total hot utility required by the system as more heat is transferred from the rectifying section to the stripping section. The total utility actually increases because the HIDC model perturbs the optimized pump-around duties. Total Hot Utility Required B) Product flowrates as more heat is being integrated. Only the flowrate of residue increases. These results show that separation efficiency is reduced as products can no longer be recovered. C) Gross profit decreases from conventional distillation. The compound of reduced production and increased utility makes this process uneconomical. A) Utility required by the system as more heat is transferred from the rectifying section to the stripping section. Energy can be saved compared to the conventional method. B) Product flowrates as more heat is being integrated. The residue increases while other products decrease. This is undesirable. B B A A)Utility required by the system as a variable is being changed. As the variable is being reduced, the hot utility is increased by approximately 20 MW. This is an undesirable trend. B) Gas Oil and Residue flowrates as a key variable is changed. As the key variable is reduced, gas oil production increases & residue decreases by about 5000 bbl/day. This is desirable since gas oil is more profitable. D) Gross profit increases as the key variable is changed The max profit was found to be about a $640,000/year increase over the conventional method. C) Utility cost increase and product profit increase as the key variable is changed. As the key variable is reduced, both utility costs and product profits increase. A trade off of less than 20MW generates about $160K of additional revenue. C Key Variable D Total Hot Utility Required Production Flowrate Annual Utility Cost and Product Profit B A) Utility required by the system as a key variable is changed. As the key variable is reduced, the hot utility is decreased by up to approximately 5 MW. Product Flowrates Total Hot Utility Required Annual Gross Profit C B) Product flowrates as key variable is changed. As the variable is reduced, flowrates do not change significantly. D C) Although profit is lost due to less production of valuable products, there are significant savings from reduced energy costs. Annual Utility Cost and Product Profit D) The maximum gross profit increase over the conventional method was found to be $740,000/year. B: HIDC concept model C: HIDC developed for crude distillation Vapor Flowrate Profile T-335 Sarkeys Energy Center 100 E. Boyd St. Norman, OK 73019-1004 Phone: (405) 325-5811 cbme@ou.edu Annual Gross Profit Kerosene Flowrate B Temperature Profiles Compressor Annual Gross Profit Product Flowrates C C) Even though energy was conserved, the costs saved were not enough to make up for the profits lost to the decrease in non-residue products. The gross profit increase compared to the conventional method was found to be approximately -$2.7 million/year when 0.5 MW heat integrated.