Pyrolysis plant

The design of a pyrolysis oven is special and depends on complete sealing, with no ingress of air and with the waste products continuously being removed with a purge of N2. This process forms a product, which when exposed to air, can absorb O2 followed by evolution of heat, which must be dissipated, failing which a fire may occur. 

---

Enerco, Inc. (Yardley, Pennsylvania) has a 600 tine/d demonstration pyrolysis plant located in Indiana, Pennsylvania. The faciUty operated 8 h/d, 5 d/wk for six months. The process involves pyrolysis in a 5.4 t/d batch-operated retort chamber. The heated tines are broken down to cmde oil, noncondensable gases, pyrolytic filter, steel (qv), and fabric waste. In this process, hot gases are fed direcdy to the mbber rather than using indirect heating as in most other pyrolyses. The pyrolysis plant was not operating as of early 1996. 

Data for the Wastewater Stream of Tire Pyrolysis Plant... 

Rail transport from many pyrolysis plants... 

Regional networks of pyrolysis plants could be established to provide oil to a central steam reforming facility. The... 

In the U.S., the largest pyrolysis plant is ENCOAL Corp. s 1000 ton coal/day pyrolysis plant, which began operation in 1992 under a cooperative agreement with the U.S. Department of Energy.14... 

Iron (II) chloride solution, for possible treatment in a pyrolysis plant or, more probably, for the production of flocculation chemicals used in sewage water treatment... 

Production Costs. The effect of varying severity on ethylene production costs is given in Figure 2. Both premium and fuel by-product situations are covered. The curves apply to a billion lb/yr European naphtha pyrolysis plant. 

Generally, most pyrolysis systems have produced similar yields. Thus, it is important that any successful pyrolysis plant make provisions for selling the byproducts, especially the char. 

At this time, there has been very limited commercial operation of pyrolysis plants in the United States. The primary barriers are economic and technical. In particular, there has yet to be a commercial demonstration of a process to economically upgrade the carbon black to a high-quality profitable by-product. Until such sustained commercial operation occurs, any potential non-economic barriers constitute a moot point. 

A pyrolysis plant thermally decomposing tires into products. 

For the primary step in the overall pyrolysis plant, the feedstock must be vaporized, if in liquid form, then mixed with steam, and finally preheated to the reactor temperature. When the feedstock (e.g., ethane or propane) is in gaseous form, vaporization is usually achieved by simple heat exchange with other product components such as condensing propylene. To vaporize liquid stocks such as naphthas, higher temperatures must be used. These feeds may be partially preheated before entering the furnace itself and then fully vaporized as they flow through the convective zone of the furnace. Typical furnace and tube geometries are shown in Fig. 4. 

FIGURE 3 Simplified flow sheet of a general pyrolysis plant. 

Multiple pyrolysis furnaces are employed in an industrial pyrolysis plant in order to maintain reasonably constant production levels, even when one furnace is shut down for decoking or maintenance repairs. The coils or tubes in a furnace or the transfer-line exchanger must... 

The gases from the scrubber-condenser contain the noncondensable gases, low-boiling organic vapors, and water vapor. A portion of the gases is used to heat the wood dryer, and the remainder is available as a fuel for other purposes, but it is desirable that it be used near the pyrolysis plant. 

Figure 5.6 Overall view of pyrolysis plant of waste plastics in KIER process...

In particular, as far as the plastic catalytic degradation is concerned, there are various possible scenarios. In large urban areas the best approach probably is to build a plastic waste pyrolysis plant in an acceptable near area at not to great distance, in order to minimize transport cost of the plastic waste. In that case, safety and environmental concerns of such a new plant should first be denied with satisfactorily before the new plant can get the go-ahead. Near refineries however, the best approach might be to co-feed plastic waste with oil fractions into refinery crackers, or even have a unit of pure thermal pyrolysis first with the produced wax-type fraction to be upstaged in another reactive refinery process. In the first case of co-feeding, a lot of research has to be carried out, addressing aspects of defluidization mainly, before an alteration of a process of the scale of FCC units can go ahead. 

Pyrolysis of PET under mild conditions predominantly forms terephthalic acid (TPA). Since TPA easily sublimes it is often found in the condensing units of pyrolysis plants. Under high-severity conditions however, little TPA is observed. This is because at higher temperatures TPA is decomposed into benzene, carbon dioxide and benzoic acid (Figure 15.3) [2]. 

The pyrolysis of PET by Sakata [3] has been found surprisingly to yield no liquid products. It is widely known that compounds that undergo sublimation, such as tereph-thalic acid and benzoic acid, are produced by the thermal decomposition of PET and this causes problems in plastic pyrolysis plants. Interestingly Yoshioka et al. [4] found that the addition of calcium hydroxide (slaked lime) gives high selectivity for benzene formation without producing sublimation compounds such as terephthalic acid. The yield of benzene is around 35 wt% at 700°C and a 10.0 calcium hydroxide/PET molar ratio. 

Typical input specifications for BP s Grangemouth pyrolysis plant are shown in Table 15.3. 

Problems with batch pyrolysis plants are often mechanical in nature and are related to residue extraction problems, coking/fouling of heat exchanging surfaces, corrosion by... 

Extmders are often used in continnons pyrolysis plants for supplying a molten stream of plastic to the main pyrolysis vessel. The extmder may also be vented to eliminate HCl (from PVC) and water vaponr from the waste plastics. In contrast to conventional extmsion, there is no need to bnild np high melt pressnre or to shear the polymer. These pyrolysis extruders are more like heated augers than polymer processing eqnipment. 

For large-scale continuously operating pyrolysis plants, a flnidized-bed reactor has numer-ons advantages such as improved heat transfer to the plastic, continuous dosing of catalyst and continnous coke removal. Fluidized-bed processes are however not efficient when applied on a relatively small scale. 

Figure 15.5 Close-up of pyrolysis chamber of commercial plastics pyrolysis plant which can convert 10 tonne of unwashed, mixed plastics into 10000 L of diesel fuel per day. (Reproduced by permission of Ozmotech Pty Ltd)...

Figure 15.6 Process flow for commercial pyrolysis plant (Thermofuel ) for converting waste plastics into diesel fuel. The plastic is heated to 375-425°C and the pyrolysis vapours are catalytically cracked and then selectively condensed. Note that the pyrolysis vessel is purged with nitrogen gas and that the hot pyrolytic vapours pass from the pyrolysis vessel to the catalytic reaction tower where they are cracked and reformed to give a high-purity diesel stream. (Reproduced by permission of Ozmotech Pty Ltd)...

At present several pyrolysis plants have been built based on different processes such as the BASF pyrolysis process, the BP University of Hamburg fluidized-bed pyrolysis process, the VEBA hydrogenation process, and several more are under way [4, 5]. 

---