Carbon Rejection Technologies

The main characteristics of carbon rejection technologies are (Solari et al., 1997  

Based on the removal of carbon in the form of coke with low atomic H/C ratio or in the form of asphalt (in the case of deasphalting), producing a moderate yield of liquid products. 

Important process for residue conversion and is the most common method used commercially. 

Thermal cracking of residue is carried out at relatively moderate pressure and is often called coking process. 

Use temperatures between 480°C and 550°C and vapor phase residence times of 20 s or more, providing a significant degree of cracking and dehydrogenation of the feed, which makes subsequent processing more cumbersome and produces low-value by-products such as gas and coke. 

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All around the world there exists an installed capacity to process residue utilizing solvent deasphalting as a carbon rejection technology followed by hydrotreatment of the deasphalted oil (DAO) or the residual. Severity of the hydrotreating stage depends on the downstream use of the hydrotreated DAO or the residual, which can be used as feedstocks to catalytic cracking/ hydrocracking or as components of low sulfur fuel. 

Hydrogen addition and carbon rejection technologies for upgrading of... 

Eigures 2.5 and 2.6 show the combinations of these carbon rejection technologies. The final products coming from the different processes are integrated, when possible, to produce upgraded oil. 

Combination of Both Hydrogen Addition AND Carbon Rejection Technologies... 

Technologies for upgrading heavy crude oils such as heavy oil, bitumen, and residua can be broadly divided into carbon rejection and hydrogen addition processes (Chapter 8). Briefly, carbon rejection processes are those processes in which a carbonaceous by-product (coke) is produced along with distillable liquid products. On the other hand, hydrogen addition processes involve reaction of the feedstock with an external source of hydrogen and result in an overall increase in H/C ratio of the products as well as a decrease in the amount of coke produced. 

Figures 2.8 and 2.9 illustrate some of the process schemes of technologies based on carbon rejection and hydrogen addition that can be combined. Figure 2.10 shows other possible combinations between the different upgrading technologies.

Chapter 2 reports some aspects of the commercially available process options for upgrading of heavy petroleum. The common carbon rejection and hydrogen addition routes as well as combined process schemes are described. Recent technologies without commercial application are also covered. 

Vourch et al49 studied the applicability of the RO process for the dairy industry wastewater. The treated wastewater total organic carbon (TOC) was <7 mg/L. It was found that in order to treat a flow of 100 m3/d, 540 m2 of the RO unit is required with 95% water recovery. Dead-end NF and RO were studied for the treatment of dairy wastewater.50 Permeate COD, monovalent ion rejection, and multivalent ion rejection for the dead-end NF were reported as 173-1095 mg/L, 50-84%, and 92.4-99.9%, respectively. When it comes to the dead-end RO membranes, the values for permeate COD, monovalent ion removal, and multivalent ion removal were 45-120 mg/L, >93.8%, and 99.6%, respectively. Membrane filtration technology can be better utilized as a tertiary treatment technology and the resultant effluent quality will be high. There can be situations where the treated effluents can be reused (especially if RO is used for the treatment). 

Due to the operating requirements of PEM stack technology, shift reactors and a carbon monoxide removal step are required to produce reformate of sufficient quality. Similarly, the stack operating temperature and its humidity requirements require a water management system as well as radiators for heat rejection. Some developers are developing pressurized systems to the benefit from higher reactant partial pressures on both anode and cathode. Fuel processing for PEM APU systems is identical to that needed in residential power or propulsion applications. 

Hagmeyer G., Gimbel R. (1993), Rejection of carbonic acid species in (reverse osmosis) and nanofiltration, Proc. of AWWA Membrane Technology Conf., Baltimore, Aug 93, 251-257. 

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