The energy efficiency section will focus on the minimising of the process heat & electrical energy requirements so that emissions from utility supplies may also be minimised.
Energy integration across any site can reduce the need for energy input to the plant - if we consider the addition of a new process unit, this may provide a source of waste heat which can be utilized elsewhere in the refinery and as a result eliminate the need for continuous use of a process heater elsewhere.
It is important to note that the process plants must maintain good operability -- able to start up independently and maintain availability.
However, if the plant in question is able to operate with fewer process heaters in operation, then clearly the energy demand of the plant will be reduced.
Carbon capture and storage has the advantage of being applicable to almost all processes in some form or another.
Taking a closer look at the options for carbon capture and storage for CO2 emissions management: CCS can be applied to a wide range of large single-point sources, such as process streams, heater / boiler exhausts and vents from a range of high CO2
Once captured the CO2 is compressed, dried and transported to a suitable storage location such as saline aquifer, depleted oil field (where enhanced oil recovery could be employed) and depleted gas fields.
Each CCS route described below is really a group of technologies based on similar process circumstances.
A. Pre-Combustion CO2 Capture
Brief Process Description
The feedstock (solid or gaseous) is fed to an oxygen (or air-blown) pressurised gasifier where it is converted to syngas. The syngas is then passed through a shift reactor which increases the hydrogen and CO2 content of the syngas. This high-pressure, high-temperature syngas is cooled, before being solvent washed to absorb the CO2 -- leaving a relatively pure hydrogen stream. The CO2 rich solvent stream is regenerated to release a CO2 stream which can be dried and compressed for export.
This process offers an interesting integration potential as it generates a pure high-pressure hydrogen stream and the syngas cooling train produces significant quantities of steam (HP, MP, LP).
Possible application of pre-combustion carbon capture would be a new power plant in which the hydrogen rich stream is combusted in a gas turbine and the steam raised during syngas heat recovery is utilised, along with heat recovered from the gas turbine exhaust, in a steam turbine to form a combined cycle plant such as an IGCC (integrated gasification combined cycle).
Coals, petcoke, fuel oils, municipal solid waste and biomass can be used as gasifier feedstock.
Natural gas and light liquid feedstocks can be used with a reformer.
A range of alternative technologies such as membranes and pressure swing absorption (PSA)
B. Post-Combustion CO2 Capture
Post combustion carbon capture is typically associated with large retrofit power projects or new high carbon footprint power plants. Post-combustion CO2 capture is a simpler system than the one implemented in pre-combustion CCS and can be associated to almost any type of combustion system. Variants:
A range of processes exist utilising different solvents: MEA, ammonia and even sea water.
For high sulphur feeds the process may be coupled with a flue gas desulphurisation unit allowing the direct contact cooler to be eliminated.
C. Oxyfuel Combustion CO2 Capture
A wide range of fuels can be used in an oxyfuel flowscheme.
Environmental issues will continue to be at the forefront of the challenges facing the Oil & Gas Industry. It will be important to maintain the level of research & development into means of reducing emissions, increasing energy efficiency and exploring all possible renewable energy sources. The 2nd Green Refining & Petrochemicals Forum to be hosted by Euro Petroleum Consultants next June in Dubrovnik (17th June 2011) will address many of these key topics in addition to latest technologies, issues, trends, regulations and strategies for reducing greenhouse gas emissions, including:
Energy Efficiency Improvement
CO2 Capture & Sequestration
Renewable Energy Sources Including Cogeneration