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Considering the enormous amounts of thermal energy and stripping steam required for crude distillation unit (CDU) throughputs, are there any new crude oil processing schemes for reducing CDU operating costs?

Dec-2022

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Jeffrey Zurlo, SUEZ Water Technologies & Solutions, jeffrey.zurlo@suez.com

Previous responses around the crude preheat systems have already mentioned mechanical design changes to the heat exchange equipment and using cleanings to recover heat transfer. An additional technique useful is to inject chemical treatments into the preheat to reduce or prevent deposition when heat transfer loss is the result of fouling build-up on the heat transfer surfaces. Ideally, these chemistries would be applied to prevent any deposition and always maintain the maximum heat transfer possible. While sometimes this can be achieved, the more common scenario is a combination of preventative treatment to slow down the rate of heat transfer loss and curative mechanical cleanings during operation to restore heat transfer to clean conditions. This most often achieves the optimal energy reduction and lowest overall cost of operation when all factors are considered. Techno-economic modeling of the preheat and crude furnace is used to reveal when cleaning individual exchangers will provide an economic benefit through recovered heat transfer and measuring the fouling tendency of the crude oil blends processed can be used to manage the chemical treatment program.

Regarding stripping steam optimization, it is suggested that a close eye is kept on the impact to the salting tendency of the distillation tower top section and overhead condensing system be considered and measured. Changing the balance of water to hydrocarbon in the tower top can change the salting characteristics and result in salt-related corrosion in new areas of the tower. This can be identified and managed through a combination of electrochemical modelling and chemical treatment selection to ensure system protection in the face of changing operating conditions and contaminant concentrations.

Dec-2022
Jagannadh Sripada, KBC (A Yokogawa Company), Jagannadh.Sripada@kbc.global

Due to the high-energy consumption of crude distillation units (CDU) and vacuum distillation units (VDU), energy reduction is essential to meet emission targets and reduce energy costs in the refining industry. Three key aspects of a new design or future revamp scenario(s) are as follows:

Configuration Recent developments in progressive crude distillation methodology make it a viable process to be considered during the design stage to potentially save utility and perhaps better yields. However, the initial Capex could be higher for such configurations, and the sensitivity of benefits on the type of crude should also be kept in mind.

Depending on location and pricing, refineries should evaluate their overhead vacuum configuration. Replacing the last stage of ejectors with liquid ring vacuum pump (LRVP) has been beneficial for refineries in the past, and the configuration is to be carefully evaluated and selected based on steam, cooling water and, electricity prices.

Heat integration Optimising heat recovery from the preheat train via a revamp could include utilising spiral and plate and frame heat exchangers at select locations, adding extra heat transfer surface area to existing heat exchangers, installing new exchangers, and more.

Process integration between CDU and VDU to save fuel, periodic re-evaluation of minimum approach temperature based on energy costs, and utilisation of pinch technology to identify opportunities should be beneficial to refineries. Monitoring heat exchanger fouling, online cleaning, and an optimised cleaning schedule will minimise fuel costs and emissions. Evaluating opportunities to utilise the product heat can include providing hot feed to downstream units or using that heat to preheat the crude at CDU.

Distillation column optimisation Reduce the operating pressure of the atmospheric column during winters to benefit from lower temperature cooling water. APC can be used to automate the minimisation of pressure to great effect.

The latest high efficiency and low DP trays and the replacement of tray sections with packings usually help refiners increase throughput, but small gains in energy can also be achieved via such modifications.

Dec-2022
Marcello Ferrara, ITW Technologies, mferrara@itwtechnologies.com

The CDU is the most energy-intensive process in a refinery (also one of the largest in the whole process industry), with its performance affecting refinery-wide efficiency. Average CDU energy consumption is estimated to be over 192 TWh/y for US refineries (DOE, 2006). Among the CDU asset, the preheat train (PHT) is the most sensitive. If working improperly, it will predicate a series of chain effects: extra CO2 emissions, reduced flow, extra furnace fuel consumption, drop in furnace inlet temperature (FIT), production loss, and reduced throughput to the point that the refiner will shut down the fouled unit for equipment cleaning due to unsustainable fouling conditions.

Formerly, Van Nostrand et al. (1981) estimated that process side fouling cost US refineries around $1.36 billion per year and $861 million due solely to PHT fouling. Currently, these numbers, corrected for inflation and current energy costs, are superior by at least one order of magnitude. The fouling problem is so important that its mitigation in CDU operations could lead to over 15% fuel savings. As fuel consumption for the atmospheric column’s furnace represents around 4% of total refinery throughput, 15% fuel savings in a 500,000 bpd facility equates to more than $347 million in savings per year.

Savings are even higher when considering that the carbon tax can reach $80 per ton or more (depending on refinery location). ITW has developed and patented its Online Cleaning technology, which can clean an entire production unit on a 24-hour feed-out/feed-in basis. The technology will allow refineries to recover losses in one day while reducing emissions and eliminating waste. Online Cleaning technology helps target sustainability development goals (SDGs) while also serving as a tool to improve Operational Excellence, rather than an alternative to mechanical cleaning.

Dec-2022
Kevin Clarke, Imubit, kevin.clarke@imubit.com

It has always been the case that the simplest way to cut your energy cost is to shut down the unit — obviously not a realistic approach, so the industry has focused on cutting energy costs by improving the efficiency of use for many decades. Many energy management and optimisation systems evolved to support this process, but one area remained very hard to define: how do you know whether that last MMSCFD of fuel gas or last lb/hr of steam you conserved cost you more in unit yield recovery? Or, if you were to spend more energy, could you gain more economic value in throughput or yield recovery? And how does that change as the cost of carbon emissions increases?

Offline simulation models have been built for many years, with engineers working tirelessly to try to understand this relationship, but the optimum is continuously changing with economics, feed rates, feed quality, and ambient conditions. Today, for the first time, enabled by advances in computer capabilities and artificial intelligence, the most forward-thinking refinery operators are using leading edge, deep reinforcement machine learning models to close this yield/energy/emissions cost trade-off in real-time, in closed-loop.

Dec-2022
Sunil Kumar, CSIR Indian Institute of Petroleum, sunilk@iip.res.in

It is reported that spirocyclic polymers with N-aryl bonds can fractionate light crude oil into light fractions consisting of molecules’ carbon number of 12 or a boiling point less than 200°C in the permeate and heavy molecules. The researchers say that, although additional research and development will be needed to advance this to an industrial scale, the new membrane could replace some conventional heat-based refining processes in the future by developing a hybrid energy-efficient technology consisting of membrane and distillation for crude oil refining (www.imperial.ac.uk/news/199934/new-membrane-could-emissions-energy-refining/New membrane could cut emissions and energy use in oil refining).

The application of a divided wall column (DWC) is also reported in one journal article for crude oil distillation to reduce energy consumption. However, the results have not been validated and compared with the actual industrial atmospheric and vacuum distillation unit (AVU) [Young Han Kim (2017): Energy Saving in a Crude Distillation Unit with a Divided Wall Column, Chemical Engineering Communications, DOI: 10.1080/00986445.2017.1379400]. CSIR-Indian Institute of Petroleum, Dehradun, has also developed a new crude oil processing method to reduce operating costs and GHG emissions. The similar topology of the developed method of an existing CDU ensures the implementation for revamping the existing and designing the grass-root.

The techno-economic study using the commercial CDU configuration showed a potential to reduce the ADC bottom stripping steam by 80-100% and energy cost by 11-16%. The lower vapour flow rate in the section above the flash zone and higher flow rate in the stripping section provide the opportunity to increase throughput and address the poor vapour-liquid contact problem in the stripping section of the ADC [Kumar, Sunil, Avinash S. Mhetre, Comparative techno-economic evaluation of potential processing schemes for petroleum crude oil distillation, Results in Engineering (2022): 100480].

Dec-2022
Roberto Tomotaki, Becht, rtomotaki@becht.com

Maintaining the crude preheat exchanger train at optimum performance. Third-party monitoring tools such as the proprietary HTRI SmartPM or Hexxcell’s Studio are two examples of industry available tools which help identify the exchanger(s) and optimum timing of the cleanings to optimise train performance. Once a cleaning decision has been made, the cleaning method is also very important. There have also been advancements in cleaning technology, such as ultrasonics and robotics, which return the exchangers to a rarely achieved near clean design condition.

Becht’s Bundle Technology Upgrade (BTU) programme helps identify the bundle technology best suited for the current operation. Exchangers designed decades ago most likely are not the optimum design. Bundle design upgrades such as helical baffles or enhanced tubes can significantly increase the exchanger performance with relatively small incremental investment. This is especially applicable when replacing a bundle at the end of its life.

Dec-2022