NOVELTY - Transforming a single reactor line (1) into a double reactor line involves adding in front of existing single reactor line a another single reactor line; or by transforming an existing single reactor line having at least 6 legs into a double reactor line. The existing single reactor line is equipped with a flash tank (40) for separating solid polymer product from flash vapour that is sent to a system of at least two separating columns allowing the separation of its constituents into monomer, diluent and comonomer.    USE - For transforming a single reactor line into a double reactor line to form double reactor system useful for preparing bimodal polyethylene resin (claimed) and olefins such as 2-8C olefin e.g. ethylene, propylene, butylene, pentene, butadiene, isoprene, and 1-hexene.    ADVANTAGE - The process easily provides double reactor line starting from an existing reactor line. The complex downstream equipment is correctly dimensioned, the production remains unchanged and cost is minimal. The method provides double reactor line that separates the effluent into their various components and re-injects them into reactor each separately at the optimal point within the reactor.    DETAILED DESCRIPTION - Transforming a single reactor line (1) into a double reactor line involves adding in front of existing single reactor line another single reactor line that is either smaller than or of same size as the existing reactor line; or by transforming an existing single reactor line having at least 6 legs into a double reactor line. The existing single reactor is transformed by rearranging the connection between vertical legs to obtain two separate reactor line reactors, where the first reactor line is smaller than or of the same size as the second reactor line; by adding a pump to the separated reactor line; and by adding a continuous transfer line to transport product from the first to the second reactor line. The existing single reactor line is equipped with a flash tank (40) for separating solid polymer product from flash vapour, and the vapour is sent to a system of at least two separating columns allowing the separation of its constituents into monomer, diluent and comonomer. The first reactor line has a smaller capacity than that of the second reactor line. The six legs single reactor line is transformed into a double reactor line by suppressing connecting segments of the existing reactor line, and by implementing connections. INDEPENDENT CLAIMS are included for the following:    (1) a double reactor system obtained from transforming single reactor line into double reactor line; and    (2) use of the double reactor system involving separating effluent products into monomer, diluent and comonomer and recycling products back to the reactor lines, where the monomer being sent downstream of the circulating pump in both reactor lines, the diluent being recycled upstream of the circulating pump in both reactor lines and the comonomer being optionally sent to only one of the reactor lines downstream of the circulating pump.    DESCRIPTION OF DRAWING(S) - The figure shows a simplified configuration of the two-reactor line system.    first reactor line (1)    second reactor line (2)    cooling jacket (11, 21)    circulating pump (15, 25)    transfer line (16)    settling line (26)    flash tank. (40)