Pyrolysis continued feedstocks

For safe disposal of the products without any adverse effects to the environment, such as recycling and subsequent repolymerization, recycling to olefinic feedstock by pyrolysis, continued burial in landfill sites, incineration, and use of environmentally degradable polymers... 

Until 1960, coal was the source material for almost all benzene produced in Europe. Petroleum benzene was first produced in Europe by the United Kingdom in 1952, by Erance in 1958, by the Eederal Republic of Germany in 1961, and by Italy in 1962. Coal has continued to decline as a benzene source in Europe, and this is evident with the closure of coke ovens in Germany (73). Most of the benzene produced in Europe is now derived from petroleum or pyrolysis gasoline. In Europe, pyrolysis gasoline is a popular source of benzene because European steam crackers mn on heavier feedstocks than those in the United States (73). 

D. P. Serrano, J. Aguado, J. M. Escola, and E. Garagorri, Conversion of low density polyethylene into petrochemical feedstocks using a continuous screw kiln reactor, J. Anal. Appl. Pyrolysis, 58-59, 789 (2001). 

Figure 15.4 A schematic of a typical continuous stirred tank pyrolysis process. Legend 1 pyrolysis vessel with internal agitator 2 catalyst chamber 3 plastic feedstock hopper 4 char auger to remove solid residue 5 agitator drive motor 6 lower temperature sensor 7 upper temperature sensor 8 burner for furnace 9 feed auger for plastic feedstock 10 condenser cooling jacket 11 condenser 12 oil recovery tank (adapted from Saito, K. and Nanba, M., United States Patent 4,584,421 (1986) Method for thermal decomposition of plastic scraps and apparatus for disposal of plastic scraps )...

A 20 t/day plant (6000 t/yr) is equipped with two pyrolysis vessels (with dimensions of 2800 mm ID and 2000 m height). The vessels are fed with molten plastics by four extruders each with a capacity of 250 kg/h. The plant runs continuously and can feed waste plastics and discharge the solid residue while the plant is running. The liquid fuels are fractionated in a fractionation tower. The plant produces a liquid fuel yield of up to 80% (by weight), depending on the nature of the feedstock. 

Mechanistic modeling has been useful in studying pyrolysis kinetics at low conversion (4,5,6). Few attempts have been reported at the high conversion levels of commercial cracking (7). This stems from the large number of species and free radicals and of their associated reactions, which increases substantially with conversion and leads to excessive computation time. In addition, when one considers that precise pyrolysis mechanisms, for even a simple feedstock such as propane (8), are still subject to dispute, it is clear that more empirical models will continue to dominate commercial applications. 

The test rig is equipped with a feedstock hopper suitable to low-bulk-density biofuels and the biomass is fed continuously into the sand bed of the reactor via an injector screw which can feed fuel either into the bottom of the bed or to about 1 meter above the air distributor. The maximum fuel mass flow rate is 90 kg/h. The feeding system consists of two screw feeders in series separated by a rotary valve. The second screw has a higher feeding rate thus it will remain almost empty and therefore is not likely to be blocked by pyrolysis products. Steam can be added to the primary air as a gasification agent. 

The pyrolysis experiments have been conducted in a horizontal tube with an internal diameter of 4 inch. The feedstock is transported through the tube by a screw. The residence time of the solids can be varied by adjusting the rotation speed of the screw. An electrical furnace supplies the heat required for the pyrolysis process, and the reactor is continuously purged with Argon. The process conditions used fw the pyrolysis experiments are given in table 1. 

ABSTRACT A novel reactor configuration has been developed in our laboratory which addresses the heat transfer limitations usually encountered in vacuum pyrolysis technology. In order to scale-up this reactor to an industrial scale, a systematic study on the heat transfer, the chemical reactions and the movement of the bed of particles inside the reactor has been carried out over the last ten years. Two different configurations of moving and stirred bed pilot units have been used to scale-up a continuous feed vacuum pyrolysis reactor, in accordance with the principle of similarity. A dynamic model for the reactor scale-up was developed, which includes heat transfer, chemical kinetics and particle flow mechanisms. Based on the results of the experimental and theoretical studies, an industrial vacuum pyrolysis reactor, 14.6 m long and 2.2 m in diameter, has been constructed and operated. The operation of the pyrolysis reactor has been successful, with the reactor capacity reaching the predicted feed rate of 3000 kg/h on a biomass feedstock anhydrous basis. 

The PDU vacuum pyrolysis reactor is a semi-continuous horizontal pilot plant reactor 3 m long with a diameter of 0.6 m and a throughput capacity of about 50 - 200 kg/h, depending on the feedstock treated. The configuration of the PDU reactor is almost the same as that of the industrial reactor, except t t the PDU has smaller agitation blades. Two types of tests have been conducted with this reactor, the cold and the hot runs. In the cold tests, the particle flow behaviour is studied by a stimulus-response technique, under different agitation speeds and feed rates. The hot tests enable the conversion to be determined as a function of the feed rate and the agitation speed. 

Integration of crop-residue pyrolysis into the vrork routine on the farm would differ depending on the crop residue available, the end-use objective, the kind of farm, and the weather zone in which the farm is located. A 10 kg/h unit would require well over a year to process the crop residue from the 50 ha farm discussed earlier. A 50 kg/h kiln operating continuously would process the same amount in 100 days The resulting char could be stored more easily than the feedstock. 

Table III shows the effect of shifting furnace operation from propane fresh feed to ethane. Data are from Schutt and Zdonik (54). The reduction of propylene yield from ethane to negligible levels in favor of increased ethylene production cannot be done if a plant has propylene commitments. Because propylene requirements cannot be satisfied with ethane feed, Ericsson (14) has concluded that propane will continue to be the preferred feedstock to make ethylene. Actually, 85% of the U.S. ethylene plants are located in the Gulf Coast area so that they can obtain and operate on economical ethane and propane feeds. The need for propane pyrolysis has resulted in a renewal of experimental interest in this area, and in-depth studies have been made by Crynes and Albright (17) and by Buekens and Froment (7).

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