A carbon management system (CMS) is crucial to ensure that carbon and energy efficiency is maintained on the refinery. The CMS will be the main tool to track and improve performance. In recent years, energy management systems (EMS) have been slowly adapted by the industry, but many refineries have yet to install one. In addition, further expanding an EMS to a CMS will yield additional savings. Key to the success is the identification, measurement, and stewardship of carbon and energy related metrics.
Improvements in waste heat recovery can also yield significant energy savings in oil refineries. One specific way to improve waste heat recovery is the use of high performance heat exchangers.
The drive to fuel destruction in general and increased diesel make has resulted in hydrogen shortages in most refineries. This gap is closed by investment in hydrogen plants or by importing over the fence hydrogen. Most on purpose hydrogen used at refineries is produced in steam reformers using feeds ranging from natural gas to light naphtha as feed and fuel.
The highest carbon abatement can usually be found in the power/steam/fuel system. Some solutions are:
Cap and trade schemes or straight carbon taxes shift the cost balance between high and low carbon fuels. This will lead, at least in the areas subject to a carbon cap or tax, to a reduced use of high carbon fuels. Steam and power systems, especially the more complex ones with multiple pressure levels and extraction turbines, offer considerable savings opportunities. Condensing turbines convert less than 30% of the energy in the steam entering into power, with the remaining energy being lost into cooling water. It has become more common to integrate power generation using a gas turbine with steam generation from the turbine exhaust.
The FCC is a major source of CO2 emissions. The coke alone of a 50 000 bpd FCC unit, fed with VGO, generates 400 000 – 500 000 tpy of CO2, however there are significant potential to improve energy efficiency and reduce emissions.
Hydrotreaters and hydrocrackers
Most of the CO2 emissions generated by hydrotreaters and hydrocrackers are indirect and are related to hydrogen consumption, gas compression and stripping steam usage. Direct emissions are generally limited to reactor and fractionator preheat or reboiling. Nevertheless, once again there is potential for significant savings.
The preview carbon abatement options are all well proven technologies. In addition, there are new technologies, some of which are already being implemented on an industrial scale, while others will not become economically viable until at least 2020.
There are many reasons why not all the carbon abatement opportunities are captured at refineries. One main cause is that economic returns in the past simply were not high enough in a low energy price environment. Investment criteria tend to be rather difficult for energy improvement projects in a capital constrained environment. Some carbon opportunities are missed out because the carbon cost often is not included in the economic evaluation models.
There is a conflict between additional product quality specs as well as the drive to reduce fuel make on the one hand, and the need to reduce carbon emissions on the other hand. However, scope remains for substantial additional GHG emission reductions, at least technically. KBC estimates that the carbon reduction achievable with less than four years payback, excluding cogeneration, to be typically approximately 15%.
You can read the full article in the March Edition of Hydrocarbon Engineering.
Read the article online at: https://www.hydrocarbonengineering.com/gas-processing/26022010/greenhouse_gas_legislation_and_the_refining_industry_part_3/