Black Carbon Market – A Profitable Destiny
Published on : Wednesday 03-02-2021
The black carbon industry can offer a profitable route to add value to the bottom barrel streams, says Dr Marcio Wagner da Silva.
The Covid-19 pandemic reduced in a drastic manner the demand for crude oil derivatives and put under pressure the refining margins of a sector that already was suffering with low profitability in the last years. Despite recovering after August, the difficulties faced in the first semester of 2020 indicate the necessity to reach participation in markets with more resilient demand like petrochemicals and special derivatives.
Refiners relying on Fluid Catalytic Cracking (FCC) units in their refining hardware enjoy great operational flexibility once these units are capable to produce high quality intermediate streams which can be applied to produce petrochemicals like Propylene and transportation fuels from bottom barrel streams, contributing to improve the refining margins.
An attractive alternative to refiners relying on FCC units is the production of aromatic residue to the black carbon market, especially considering the limitation imposed by the IMO 2020 to apply residue streams as diluent to the new marine fuel oil (Bunker). The black carbon market is projected to reach close to USD 14 billion in 2021 with an annual growth of 4.6% between 2016 and 2021 (according to data from Markets & Markets website, 2020). The black carbon is applied as raw material to growing industries like tires, rubber, metallurgy, inks, construction, etc.
Under the current scenario, the black carbon market can offer a profitable alternative to refiners capable of meeting the specifications of the aromatic residue in FCC units to provide adequate destiny to bottom streams.
Fluid catalytic cracking technologies – A flexible refining technology
Fluid Catalytic Cracking (FCC) is one of the main processes, which gives higher operational flexibility and profitability to refiners. The catalytic cracking process was widely studied over the last decades and became the principal and most employed process dedicated to converting heavy oil fractions in higher economic value streams.
The installation of catalytic cracking units allows refiners to process heavier crude oils and consequently cheaper, raising the refining margin, mainly in higher crude oil prices scenario or in geopolitical crises that can cause difficulties in accessing light oils. The typical Catalytic Cracking Unit feed stream is gas oils from the vacuum distillation process. However, some variations are found in some refineries, like sending heavy coke naphtha, coke gas oils and deasphalted oils from solvent deasphalting units to processing in the FCC unit.
In a conventional scheme, the catalyst regeneration process consists of the carbon partial burning deposited over the catalyst, according to chemical reaction below:
C + ½ O2 → CO
The carbon monoxide is burned in a boiler capable of generating higher pressure steam that supplies other process units in the refinery.
An important variation of the fluid catalytic cracking technology is the residue fluid catalytic cracking unit (RFCC). In this case, the feedstock to the process is basically residue from the atmospheric distillation column. Due to the high carbon residue and contaminants (metals, sulphur, nitrogen, etc.), some adaptations in the unit are necessary, like catalysts with higher resistance to metals and nitrogen and catalyst coolers. Furthermore, it is necessary to apply materials with most noble metallurgy due the higher temperatures reached in the catalyst regeneration step (due the higher coke quantity deposited on the catalyst), which raises significantly the capital investment to the unit installation. Nitrogen is a strong contaminant to the FCC catalyst because they neutralise the acid sites of the catalyst which are responsible for the cracking reactions.
When the residue has high contaminants content, it is common for the feed stream treatment in hydro treating units to reduce the metals and heteroatoms concentration to protect the FCC catalyst.
Typically, the average yield in fluid catalytic cracking units is 55% in volume in cracked naphtha and 30% in LPG.
The decanted oil stream contains the heavier products and has high aromatic content; it is common that these products are contaminated with catalyst fines and normally this stream is directed to use like fuel oil diluent, but in some refineries, this stream can be used to produce black carbon.
Light Cycle Oil (LCO) has a distillation range close to diesel and normally this stream is directed to treatment in severe hydro treating units (due to the high aromaticity). After this treatment the LCO is sent to the refinery diesel pool.
Heavy cracked naphtha is normally directed to refinery gasoline pool; however, in scenarios where the objective is to raise the production of middle distillates, this stream can be sent to hydro treating units for further diesel production.
The overhead products from the main fractionator are still in gaseous phase and are sent to the gas separation section. The fuel gas is sent to the refinery fuel gas ring, after treatment to remove H2S, where it will be burned in fired heaters while the LPG is directed to treatment (MEROX) and further commercialisation. The LPG produced by FCC units has a high content of light olefins (mainly propylene) so, in some refineries, the LPG stream is processed in a propylene separation unit to recover the propylene that has higher added value than LPG.
Cracked naphtha is usually sent to refinery gasoline pools which are formed by naphtha produced by other process units like straight run naphtha, naphtha from the catalytic reforming unit, etc.
Meeting the requirements to reach black carbon market
The black carbon is composed of colloidal particles of essentially pure carbon produced through the partial combustion or thermal treatment of heavy hydrocarbons, mainly highly aromatic streams like the decanted oil produced in FCC units.
According to the market demand, the FCC units can be optimised to maximise the yield of aromatic residue. This is the less common operation mode in FCC units, where the main objective is to maximise the yield of decanted oil and achieve the quality requirements of aromatic residue.
The main difficulty to comply with the aromatic residue specification is regarding ash content in the decanted oil. This parameter is strictly related to the cyclone’s efficiency in the catalyst regeneration section. To achieve this objective some refiners apply additives to promote de ash decantation in the final tanks or specific filtration systems that require more capital spending.
Another key quality parameter to meet aromatic residue specification is the BMCI (Bureau of Mines Correlation Index) that is related to the aromaticity of the decanted oil. To achieve the current specifications of black carbon, it is necessary to achieve a minimum BMCI higher than 120. The BMCI is calculated based on viscosity of the decanted oil at the temperature of 210°F. The metal content in the decanted oil needs to be also controlled, especially, sodium, aluminium, and silicon.
The operating severity in maximum aromatic residue mode tends to be high with high TRX, high catalyst/oil ratio, and high catalyst activity. As a side effect, the rise in octane number is observed in cracked naphtha due to the incorporation of aromatic compounds in this intermediate. These operational conditions can lead to a shorter lifecycle to the processing unit, especially the bottom system of the main fractionator column and heat exchangers. However this can be managed through adequate dosage of mud dispersant and ash reductor to minimise deposition.
In maximum aromatic residue operation mode, the main restrictions are the temperature of the bottom section in the main fractionators that can lead to coke formation, metallurgic limitations in the hot sections as well as the capacity of blowers and cold area compressors. A conventional FCC unit is expected to reach a yield varying from 10 to 15% of aromatic residue (in relation to the feed).
As discussed above, the FCC units offer great operation flexibility to refiners and can raise significantly the refining margins and, according to the local market demand, the process unit can be optimised to produce different kinds of intermediates. Following recent trends, the synergy between refining and petrochemical processes raises the availability of raw materials to petrochemical plants and makes the supply of energy to these processes more reliable and at the same time ensures better refining margin to refiners due to the high added value of petrochemical intermediates when compared with transportation fuels.
Considering the current restrictions, to apply the FCC decanted oil as diluent to the new marine fuel oil, the production of aromatic residue in compliance with the quality requirements to the black carbon industry can offer a profitable route to add value to the bottom barrel streams.
Like a flexible refining technology, the Fluid Catalytic Cracking (FCC) units have a highlighted role in the future of the downstream industry, especially considering the transitive period, where the FCC units can help to supply the demand by petrochemicals without shortage of transportation fuels, while the aromatic residue production can ensure even more profitability to the unit offering noblest destiny to the bottom streams.
Gary, J H; Handwerk, G E – Petroleum Refining – Technology and Economics, 4th edition, Marcel Dekker, 2001.
Myers, R A – Handbook of Petroleum Refining Processes, 3rd edition, McGraw-Hill, 2004.
Robinson, P R; Hsu, CS – Handbook of Petroleum Technology, 1st edition, Springer, 2017.
Dr Marcio Wagner da Silva is Process Engineer and Project Manager focusing on the Crude Oil Refining Industry based in São José dos Campos, Brazil. A Bachelor in Chemical Engineering from University of Maringa (UEM), Brazil and PhD in Chemical Engineering from University of Campinas (UNICAMP), Brazil, Dr Wagner has extensive experience in research, design and construction to oil and gas industry including developing and coordinating projects to operational improvements and debottlenecking to bottom barrel units. Dr Marcio Wagner also has an MBA in Project Management from Federal University of Rio de Janeiro (UFRJ) and is certified in Business from Getulio Vargas Foundation (FGV).