MATERIALS, PLASTICS, AND PLASTIC WASTE

Technical Field

The invention relates to a process and apparatus for conversion materials of hydrocarbon origin, plastics, and plastic waste. The process comprises the steps of storing, sorting, and crushing the plastics and plastic waste, and feeding them into a reactor. The apparatus comprises a storage unit, a sorting unit, a feed unit, and a reactor.

Background Art

The pyrolysis of materials of hydrocarbon origin and plastic waste is a type of thermal technologies that is suited for conversion these materials into products with properties that are considered favourable in some respects, or into energy.

Thermal treatment technologies can be classified into the following groups: low-temperature pyrolysis, low -temperature gasification, pyrolytic gasification, conventional incineration, high-temperature gasification, plasma technology.

According to this classification, the present invention can be included in the groups of low and high-temperature gasification, where the temperature ranges are 300-650°C and 650- 1200°C. Excess air coefficient: =0, operating pressure: p ₀ = atmospheric, auxiliary flow: steam.

The state of the art of the technical field is summarised in the literature in various articles and books. One of the most important comprehensive works is the book entitled Kbrnyezettechnika [Environmental technology, Mezogazda Lap- es Kbnyvkiado Kft., 2003] by Istvan Barotfi, which lists five industrially applied pyrolysis-based processes that are worth to mention:

1. ECO-WASE process (a combination of controlled thermal oxidation and subsequent incineration).

2. Siemens process (a combination of pyrolysis and high-temperature incineration).

3. Lurgi’s process (WIKONEX; a fluid-bed unit is applied for initial thermal digestion, and subsequently the energy required for pyrolysis is provided by partial combustion of the gas and pyrolytic coke).

4. Noel’s conversion process (thermal digestion of the waste is performed in an indirectly heated rotary-drum reactor, and then - after grinding the residual coke - the waste is passed on to the flow-type gasification reactor where partial oxidation is applied for energy recovery).

5. Thermoselect process, wherein the waste is compacted and then degasified applying pyrolysis, which is followed by gasification and high-temperature combustion.

The above cited processes have the common feature that at some operational stage all of them include a pyrolysis phase operating at an excess air coefficient of X ). The above referenced pyrolytic processes also have it in common that the generated flue gases come into contact with the process gas, i.e., they are mixed. Translated to heating technology terms this means that the excess air coefficient X T). Because the composition of the waste entering the process is not known in advance, the combustion/oxidation processes are impossible to control in an optimal manner. It is especially dangerous if the composition of additional materials (additives) contained by the plastic waste is not known.

A multiple-hearth furnace for the incineration of sewage sludge filter-cake adapted to carry out such a pyrolytic process is disclosed in the patent description EP 0577759B 1. In such apparatuses, heat introduction is implemented by the oxygen-poor combustion of the gas, which means that the flue gas is mixed with the process gas.

The known processes do not provide a solution to the problem of simultaneously providing, in the same reactor space, the temperature required for the combustion of the process gas and fulfilling the temperature requirements of the process of conversion hydrocarbon derivatives. For example, let the temperature of the decomposition/transformation process be 300 °C, while the optimal temperature for the combustion of the process gas is 820-850 °C, at an incubation time of 2-3 s. It is impossible (not feasible) to simultaneously fulfil both conditions inside conventional reactors.

Processes applying rotary-drum reactors (where the flue gas does not come into contact with the flue gas originating from the process gas), however, constitute an exception to this. Such a solution is also disclosed in the document W02013/015819A1. This type of apparatus poses a different problem. The flue gas (having a temperature of 820-850 °C) heats up the external wall of the drum, but it is not possible to detect the cracks of the drum surface during operation. Another problem is that the possibilities for carrying away the process gas are limited as the capacity is scaled up. The cause of this limitation is that it is technically difficult/not feasible to increase the diameter of the connecting pipe at the output side of the reactor and to increase the diameter of the seal of the drum as the flow rate of the process gas is increased.

The objective of the invention is to eliminate the drawbacks of the technical solutions cited above and provide a process for conversion plastics of hydrocarbon origin and plastic waste into light oil, heavy oil, paraffin-type hydrocarbons, solid carbon-containing powder, and hydrocarbon-containing gas.

We have recognised that by providing the heat required by the decomposition process performed in the reactor by the energy of the gas combusted in a separate space, i.e., predominantly by combusting the process gas, and by utilising the heat generated by combusting the gas for heating a portion of the spent/cooled-off process gas coming from the reactor and reintroducing it into the reactor space applying fans, it is possible to eliminate the disadvantages of the technical solutions described above.

Disclosure of the Invention

Our invention therefore relates to a process for conversion materials of hydrocarbon origin, plastics, and plastic waste, the process comprising the steps of storing, sorting, and crushing the plastics and plastic waste, and feeding them into a reactor. The process is characterised by heating the starting material in a reactor to a temperature in the temperature range of 300- 1200°C predetermined depending on the starting material and the final product. In order to provide the heat required by the decomposition process, the cooled-down process gas is carried away from the reactor, and process gas heated up in a separate space is mixed to it in a controlled manner. In the reactor, the material is directed downwards from the top, causing the material to decompose during the process. The end products of the decomposition process, which can be light oil, heavy oil, paraffin-type hydrocarbons, process gases, and carbon-containing powders, are discharged from the reactor.

The preferred modes of carrying out the invention are presented in Claims 2-4.

Our invention further relates to an apparatus for conversion materials of hydrocarbon origin, plastics, and plastic waste, the apparatus comprising a storage unit, a sorting unit, a feed unit, and a reactor. The invention is characterised in that the casing of the reactor is constituted by the dual-wall vacuum-insulated top portion and the dual-wall vacuum-insulated bottom portion of a bell furnace, the reactor body being constituted by portions of a multi-tray, multizone multiple hearth furnace that have no casing. A respective separately controllable high-temperature circulation fan is connected to each zone, the circulation fans being connected to a condenser and also to dampers/mixing valves. Furthermore, the dampers/mixing valves are in connection with an energy centre. A carbon discharge stub adapted for carrying away the carbon-containing powder is arranged at the bottom of the bell furnace.

Preferred modes of realising the apparatus according to the invention are disclosed in Claims 6-9.

Brief Description of the Drawings

In the following, the invention is described referring to the accompanying drawings, where

Fig. 1 is the schematic flow diagram of the process according to the invention, Fig. 2 is a schematic depiction of the components of the apparatus according to the invention,

Fig. 3 shows a cross-sectional view of the reactor body arranged in a bell furnace, and Fig. 4 illustrates, in a half-section view, the configuration of the bell furnace.

Modes for Carrying out the Invention

Mixed plastic waste arrives to the storage containers 1 ’ in containers or in waste collection trucks, from where the waste material is fed to the waste sorting unit 2’. In the course of the process, in the step designated with the reference numeral 1, the materials of hydrocarbon origin, plastics and plastic waste are stored and prepared. After the preparation and sorting step, in step 2 the already homogenous-composition waste is collected in storage bins. Before entering the production process, the plastic waste is crushed to a given size. In step 3, the prepared plastic waste is compacted and is introduced into the reactor 4 at high pressure. In the reactor 4, the material is heated to a temperature in the temperature range of 300-1200°C predetermined depending on the feedstock and the final product. The temperature is determined depending on the feedstock to be transformed, and on the desired ratio of gas, light and heavy oil to be obtained.

In order to provide the heat required by the decomposition process, the cooled-down process gas is carried away from the reactor 4, with process gas heated up in a separate space being mixed to it in a controlled manner. The separate space is an energy centre 7, wherein, after cleaning the process gas, a portion of the cleaned process gas is combusted, the generated heat being utilised for heating - by means of the heat exchanger of the energy centre 7 - a portion of the process gas coming from the reactor 4. To provide the heat required for the decomposition process, the heated process gas is mixed in a controlled manner with the other portion of the process gas - coming from the direction of the reactor 4 and having lower temperature. The mixing is performed applying dampers/mixing valves 6.1, 6.2, 6.3, and thereafter the heated process gas is reintroduced into the interior space of the reactor 4.

In the reactor 4, the material is directed downwards from the top, causing the material to decompose during the process. The end product of the decomposition process, which can be light oil, heavy oil, paraffin-type hydrocarbons, process gases, and carbon-containing powder, is discharged from the reactor 4. The excess process gas generated in the reactor is passed on to a condenser 8, wherein the gas is separated into fractions while being cooled down. The light condensate oil 8.1 and the heavy condensate oil 8.2 are introduced, respectively, into a light oil container and a heavy oil container that are not shown in the drawings, carrying off the paraffin-type condensates through a condensate storage tank (not shown in the drawing) and then, via a condensate/water separator 8.3, spraying them into the process gas.

In the following, the process is described for the case of a process temperature of 600 °C. In this case, the dampers/mixing valves 6.1, 6.2, 6.3 that can be seen in Fig. 2 are applied for mixing the hot gas (having a temperature of 700-750 °C) coming from the direction of the energy centre 7 to a portion of the cooled-off process gas coming from the reactor 4 in such a manner that the resulting temperature of the gas is 600 °C. Under these conditions, water fed to the reactor 4 by a water pump 16 leaves the heat exchangers 9 as water vapour and is fed into the reactor 4 along a water vapour feed path 14, with the transformation process taking place in the reactor 4 in its presence. As a result of the transformation process, starting at the top and stepping downwards from tray to tray, a carbon powder-like material is obtained, the powder falling into a residual carbon storage tank 11, from where is it is discharged. The excess process gas leaving the reactor 4 shown in Fig. 2 is passed on to the condenser 8, wherein it is transformed by fractional distillation into light oil, heavy oil, paraffin-type hydrocarbons, and gas. From here the gas is fed to a process gas cleaner 13, followed by combusting a portion of the process gas in the process gas burner 7.1. The temperature of the flue gas leaving the energy centre 7 shown in Fig. 2 is 820-850 °C when it enters the heat exchangers 9, from where, after an incubation period of 2-3 seconds, it leaves the apparatus through a flue gas stack 10 at a temperature of 70-80 °C.

A pressure of 10’ ³ bar is provided between the dual walls of the bell furnace and is continuously monitored applying a pressure sensor. In the event of detecting a pressure rise, the decomposition process is halted, and the reactor space is deluged with CO2 gas. The essential component of the apparatus adapted for carrying out the process is the modified multiple-hearth furnace, which has been modified to enable it to perform tasks related to conversion plastic waste. (The apparatus is known in the English-, German-, and Hungarian- language literature of the field as “Multiple-Hearth Furnace”, “Mehretagenofen”, and “Tobbszintu pbrkblokemence”, respectively.) The furnace modified in such a manner will hereinafter be called a reactor 4. The reactor 4 shown in Fig. 2 consists of two main portions. One is the reactor body 4.3, which differs from the multi-tray multiple-hearth furnaces in that it does not have the casing and heating system of the latter. The casing of the reactor 4 is constituted by the dual-wall, vacuum-insulated top portion 4.1 and the dual-wall, vacuum- insulated bottom portion 4.2 of a bell furnace. The pressure between the dual walls of the bell furnace is 10’ ³ bar, with the inside surface of the external wall facing the vacuum space being covered by thermal-insulating ceramic fibre material, with a heat-reflective layer being disposed on the layer’s surface.

The top portion 4.1 of the bell furnace is lifted and lowered by a lifting machine. The reactor body 4.3 depicted in Fig. 3 has a “self-supporting” design.

This means that there is no physical connection between the liftable top portion 4.1 of the bell furnace and the components of the reactor body 4.3.

The force ensuring gas-tightness between the top portion 4.1 and the bottom portion 4.2 of the bell furnace is provided by the own weight of the bell furnace. The top portion 4.1 of the bell furnace comprises refractory masonry 4.1.1. A water seal that is 4.22 depicted in Fig. 4 and is adapted for improving the gas-tightness and safety of the furnace space is disposed along the bottom edge of the bell furnace. The dual-wall medium-pressure vacuum space is adapted to provide thermal insulation but also plays a safety role. It performs its safety function such that in the event that the vacuum is lost it immediately indicates that the surface of the bell furnace has been damaged. If the vacuum is lost, a pressure sensor triggers an alarm and immediately stops the process.

The multilevel, multi-tray core of the reactor body 4.3 depicted in Fig. 3 consists of a plurality of zones. Each zone consists of two trays, with hot gas arriving to the upper tray of each zone, and with the cooled-off process gas leaving the particular zone near the tray situated underneath it. The number of zones is determined in the design phase based on technological requirements. In Fig. 3 there can be observed how the process gas 4.3.1 is introduced into the first zone and how the process gas 4.3.4 is exhausted therefrom; how the process gas 4.3.2 is introduced into the second zone and how the process gas 4.3.5 is exhausted therefrom; and also, how the process gas 4.3.3 is introduced into the third zone and how the process gas 4.3.6 is exhausted therefrom.

The carbon-containing residues of the transformed hydrocarbon derivatives are carried off into a residual carbon storage tank 11 (shown in Fig. 2) through a carbon discharge stub 4.21 that can be seen in Fig. 4.

A respective separately controllable high-temperature circulation fan 5.1, 5.2, 5.3 is connected to each zone of the reactor 4. The circulation fans 5.1, 5.2, 5.3 are connected to a condenser 8 and also to dampers/mixing valves 6.1, 6.2, 6.3 that can be seen in Fig. 2, said dampers/mixing valves 6.1, 6.2, 6.3 further being in connection with an energy centre 7 that can be seen in Fig. 2. The dampers/mixing valves 6.1, 6.2, 6.3 are adapted for mixing the cooled-down process gas coming from the direction of the reactor 4 and the hot process gas coming from the direction of the energy centre 7.

The task of heating the process gas is performed by an external energy centre 7, with the heated process gas supplying the required energy to the reactor 4 that is in indirect connection with the flue gas. The dampers/mixing valves 6.1, 6.2, 6.3 disposed upstream of each input level are applied for mixing the heated process gas to the cooled-off gas coming from the reactor 4 space in a controlled manner, such that the required temperature can be provided at the points of introduction of the process gas 4.3.1, 4.3.2, 4.3.3. The energy centre 7 obtains the heat required for heating the process gas by burning a portion of the already cleaned process gas in a combustion chamber 7.1. The energy centre 7 comprises a process gas superheater 7.2.

The excess quantity of the process gas is fed into a storage container 18 and is subsequently utilised outside the apparatus for other purposes. The thermal energy required for starting the transformation process is provided by burning utility natural gas in a natural gas-fired supporting burner 12. In the energy centre 7 the combustion processes are controlled such that the temperature of the flue gas leaving the energy centre 7 in the direction of the flue gas stack is 820-850 °C.

The excess process gas generated in the reactor 4 is passed on to the condenser 8, wherein the gas is separated into fractions while being cooled down. The light condensate oil 8.1 and the heavy condensate oil 8.2 coming from the condenser 8 are stored in a light oil storage container and in a heavy oil storage container, respectively. The paraffin-type condensates are discharged via a condensate storage tank, which is followed by spraying them into the process gas coming from the direction of the circulation fans 5.1, 5.2, 5.3 via the condensate/water separator 8.3, or reintroducing them into the feed unit 3 ’ . In Fig. 1, the feed paths of the plastic and the hot flue gas into the reactor 4, and the path along which the cooled- off flue gas is reintroduced therein are indicated by the reference numerals 3.1, 3.2, and 3.3, respectively.

The energy centre 7 is an apparatus that is adapted to bum gases of various grades, and also pre-heated oils/heavy oils/paraffin-type hydrocarbons. The apparatus comprises a process gas cleaner 13. The gas coming from the process gas cleaner 13 is burned in a recuperative process gas burner 17. The heat exchangers 9 are adapted for feeding warm air to the gas- fired supporting burner 12 and the recuperative process gas burner 17 with the help of an air fan 15. The high-temperature flue gas of the gases burned in the burners is passed through the heat exchanger of the energy centre 7 and is exhausted into the surrounding atmosphere via the heat exchangers 9 and a flue gas stack 10. In the process and apparatus disclosed above, the principle of thermolysis/gasification is applied for decomposing the plastics; the process gas and the flue gas do not come into direct contact. We were able to implement this due to the separation/relocation of the energy supply location from the process space to a separate energy centre.