HS-FCC (High Severity FCC)
An alliance comprising of Saudi Aramco, JX Nippon Oil & Energy Corp.(JX), King Fahd University of Petroleum and Minerals, Technip Stone & Webster Process Technology and Axens has developed the HS-FCC process which is able to produce up to 25 wt% propylene by converting heavy hydrocarbon feedstock under severe FCC conditions, using a novel down-flow reactor concept.
A 3,000 BPSD HS-FCC semi-commercial plant started at the Mizushima refinery of JX group in Japan in 2011. Alongside propylene, a considerable amount of butenes, gasoline and aromatics are produced as valuable by-products. The HS-FCC product portfolio can be further increased towards propylene and aromatics by downstream conversion of its less desirable products, using proven technology approaches.
The main features of the HS-FCC process are: a down-flow reactor, high reaction temperature, short contact time and high catalyst to oil ratio (C/O). The HS-FCC process operates at high temperature and high C/O ratio resulting in two competing cracking reactions, thermal cracking and catalytic cracking . Thermal cracking contributes to the production of dry gas while catalytic cracking enhances the yield of propylene.
A down-flow reactor system has been adopted. Both the catalyst and the feed flow downwards with gravity through the reactor to minimize back mixing and obtain a narrower distribution of residence times. This maximizes the production of intermediate products such as gasoline and light olefins. The down-flow reactor allows a higher C/O ratio because the lifting of catalyst by vaporized feed is not required and the down-flow configuration ensures plug flow without back mixing.
The HS-FCC process is operated under considerably higher reaction temperatures (550 to 650°C) than conventional FCC units. Under these conditions, however, thermal cracking of hydrocarbons also takes place concurrently with catalytic cracking, resulting in increased undesirable products as dry gas and coke. Short contact time (less than 0.5 sec) of the feed and product hydrocarbons in the downer minimizes thermal cracking. Undesirable successive reactions such as hydrogen transfer, which consume olefins, are suppressed. In order to attain the short residence time, the catalyst and the products have to be separated immediately at the reactor outlet. For this purpose, a high efficiency, short residence time product separator has been developed capable of suppressing side reactions ( oligomerization and hydrogenation of light olefins) and coke formation.
In order to compensate a drop in conversion due to short contact time, the HS-FCC process is operated at a high catalyst to oil ratio (C/O). The advantage of operation at high C/O is the enhanced contribution of catalytic cracking over thermal cracking. High C/O maintains heat balance and helps minimize thermal cracking, over cracking, and hydrogen transfer reactions.
HS-FCC for propylene: concept to commercial operation
HS-FCC for Propylene: Concept to Commercial Operation