WO2018149424A1

WO2018149424A1 - Unique process produces electricity through tyre pyrolysis

Info

Publication number: WO2018149424A1
Application number: PCT/CY2017/000001
Authority: WO
Inventors: Dimitrios CONSTANTINIDES
Original assignee: Bioland Energy Limited
Priority date: 2017-02-15
Filing date: 2017-02-15
Publication date: 2018-08-23

Abstract

The recycling of vehicle tyres 'at the end of their life cycle' is a universal problem and many processes have been developed to deal with this problem including the process of pyrolysis which involves the thermochemical decomposition of rubber at elevated temperatures. Several problems are believed to hinder the technical and commercial pyrolysis systems most importantly the problems encountered in downstream processes for handling the pyrolysis products as well as the problems encountered with environmental factors. So far no unique system is known to be suitable for producing fully commercial products within the prevailing environmental laws and regulations. The proposed system which is the subject of this patent application is based on the Overall concept of putting several unit processes together to produce electrical power, which is the target end product right from the waste tyres. The system consists basically of several unit processes which are utilised to achieve three main objectives i.e. a) Producing commercial products of specific quality standards for eligible uses b) Upgrading the pyrolysis oil to a quality standard suitable for combustion as fuel in power generating engines and producing electrical power as the main target end product c) Gaseous emissions with no adverse impacts to the environment thus complying to all environmental laws and regulations applicable anywhere It is also noted that the proposed system does not require any external sources of energy and it is self-sustainable once it has been placed into operation.

Description

DESCRIPTION

Unique Process Produces Electricity Through Tyre Pyrolysis

The invention, which is the subject of this patent application, relates to a unique system for the production of electricity as the main target end product from the thermal pyrolysis of vehicle tyres 'at the end of their life cycle'.

In the proposed system the pyrolysis process is a batch process whereby vehicle tyres 'at the end of their life cycle' are thermally decomposed in a rotary steel kiln termed 'the pyrolysis reactor' to produce three basic products namely,

1. TPO (Tyre Pyrolysis Oil) which is a liquid fuel

2. Carbon Black powder

3. Steel wire, which is contained in the tyres, in the form of small pieces

The TPO is further treated in a downstream plant comprising a distillation unit and other separation systems for upgrading to make it suitable for combustion in a downstream power generation plant to produce electricity.

The various unit processes comprising the invention are described as follows:

The used tires are received in bulk in the form of cut pieces of typical size 5cm x 5cm with the steel wire remaining inside the rubber pieces. The pyrolysis cycle starts by starting up the drive of the rotary kiln and at the same time the tyre feed system which in this specific application comprises a bucket elevator, chain conveyor and screw feeder, is started up and mechanically feeds the cut tyres into the rotating reactor. The feeding stops automatically when the set tonnage is reached.

Heating is applied by circulating FG (Flue Gas) from a downstream waste incinerator through the peripheral jacket of the reactor and the reactor begins to heat up. The pyrolysis cycle temperature is controlled in accordance to the predetermined temperature-time profile which has been set in the DCS (Digital Control System) system. Typically, the temperature gradient is slow at the beginning up to 150°C, it is then increased slightly to go faster to the final pyrolysis temperature in the range of 350-450 °C. It is then held at this temperature for about an hour to complete the pyrolysis and the reactor will then start to cool down to less than 200°C at which temperature the CB/Steel wire mixture can be discharged. This is done automatically by mechanical systems.

The pyrolysis process is a batch process. In this specific application the tyre batch will be about 15 tons, and the cycle (batch cycle time) is about 18 hours, including the feed time, cooling and discharge.

All heating requirements will be effected by directing FG (Flue Gas) at about 800°C arising from the combustion of the Syngas (Non-condensable Hydrocarbon Gas) in a special combustion chamber (incinerator) maintained at 850°C to the pyrolysis reactor jacket. Only for the very first batch some Light Fuel Oil (LFO) will be used. Gaseous hydrocarbons begin to emerge at a temperature around 180 °C and directed via a separation pot to take out the impurities and / or heavy fractions (tar), to the water cooled condensers whereby they are condensed by cooling and liquefied to the liquid product i.e. raw Tyre Pyrolysis Oil (TPO) which is collected in a buffer storage vessel. The non-condensable HC (Hydrocarbon) Gases are directed via a buffer tank to the Syngas Combustion Chamber (Waste Incinerator) as shown in the Overall Process Flow Diagram, Fig.1 . The FG (Flue Gas) leaving the reactor jacket is directed to the FG treatment section prior to discharge to the atmosphere from the chimney as shown in the same Process Flow Diagram, Fig.1 .

In the plant which is the subject of this application a multiple number of pyrolysis reactors, in this specific example 1 1 reactor lines, shall be used. Apart from achieving higher production rates thus achieving economies of scale, the use of multiple reactors which can be started up sequentially and phased out by a set time interval, serves to smooth out the peaks in the evolution of the HC gas and accordingly the use of the non-condensable syngas. Thus the cycle in the second reactor will start about 2 hours after starting the first reactor, the cycle in the third reactor will start about 2 hours after the second and so forth. The starting up and loading of the reactors sequentially at pre-determined time intervals can be controlled by the DCS (Digital Control System).

After completion of the pyrolysis, the oven is cooled to less than 200 °C and the mixture of CB (Carbon Black) and steel wires is discharged and mechanically transported by chain conveyors to the buffer storage silo. From the silo the mixture is fed to a separation system comprising a vibratory screen and magnetic separator in series which separates the steel wire pieces from the CB powder. The steel which is generally dirty from carbon ash and/or rust is fed to the specially designed cleaning machine and thence into the steel baler and it is pressed into cubes of metal of approximate weight 1 -ton.

The carbon black powder is fed into a rotary mill for milling to a fine carbon black powder as shown in Fig.3A. The CB powder is then fed to a pelletizer machine in which water is injected by means of a metering pump and transformed into spherical pellets of size <1 ,0 mm. The CB pellets are then dried completely in a FBD (Fluid Bed Dryer) or rotary kiln dryer and after cooling they are packaged in 1 -ton bulk bags and/or 25kg bags as shown in Fig.3B.

Typical yields from the pyrolysis process are as follows

TPO (Tyre Pyrolysis Oil) 42-45

CB (Carbon Black) 30-35

Steel wires 12-15

Non-condensable syngas 8-10

The raw TPO fuel oil from the pyrolysis plant is pumped to storage tanks for further processing in the Distillation Unit whereby it is refined and upgraded to a specification suitable for combustion in ICE (Internal Combustion Engines) e.g. power generators for electricity production. Most typically it is upgraded by removing the light fractions (typically about 10%) and a heavy residue (typically 3-5 %) in the distillation unit and then by a series of purification steps and centrifugation to remove any residual water and solid impurities as shown in the Process Flow Diagram, Fig.4. More analytically the process shown in Fig.4 for TPO refining is as follows:

Raw TPO is initially charged into the "Dehydrator Tower" to a pre-determined level. This oil is then recirculated through a heat exchanger and then a tubular furnace and heated up to a temperature of 290°C. The "Dehydrator Tower" is subsequently maintained at this temperature and at a slight vacuum (0,7 Bar.a) drawn by a vacuum pump system, during the steady state continuous operation. During the process of heating up the oil to 290°C and keeping it at this temperature any water present in the oil will be evaporated along with the light fraction oil and condensed in a downstream water-cooled condenser and collected in the storage tank.

At the beginning, after the oil in the "dehydrator tower" has reached 290°C it is pumped into the "Distillation Tower" to a pre-determined level. More TPO is fed into the "dehydrator" and heated up as before until the set levels in both units have been attained. From the bottom of the "Distillation Tower" the oil is recirculated to the top via the tubular furnace until it reaches the temperature of 380°C. The "Distillation Tower" is subsequently maintained at this temperature and at a slight vacuum (0,7 Bar.a) drawn by a separate vacuum pump system, during the steady state continuous operation. At this temperature the long-chain hydrocarbons will be cracked down to smaller chain i.e. lighter fraction oil (diesel). The hot oil gas from the top of the "Distillation Tower" is first driven into a heat exchanger and preheats the oil coming from the "dehydrator" (before the latter goes into the tubular furnace for further heating) and subsequently directed to a water- cooled shell and tube condenser and collected as DTPO (Distilled Tyre Pyrolysis Oil) in the storage tank. The heavy oil residue from the bottom of the "distillation tower" is pumped via a shell and tube cooler to a storage tank.

The approximate product split from the process described above will be as follows: DTPO of the Diesel range: 87 % Light Fraction Oil: 10 % Heavy Oil residue: 3 % The DTPO will have a yellowish colour as opposed to black raw TPO and it will have the properties of typical diesel used for internal combustion engines (ICE) but it will probably contain some minute solid particles e.g. carbon etc which might have been entrained in the oil gas. Another possible deviation from the EU Standard for Diesel for ICE, is in the sulfur content.

Various downstream processes may be utilized to improve the quality of the distilled TPO and in this specific application the following processes are utilised:

1 . Alkali wash: to lower the sulfur content

2. Acid wash: to neutralize any residual acid

3. Activated clay: to remove solid particle impurities e.g. carbon ash etc.

The DTPO is passed through suitably designed tanks to perform the above operations in series prior to passing it through a pressure filtration unit e.g. a filter press or a cartridge filter as shown in the Process Flow Diagram, Fig.4. In the described plant there will also be a specially designed catalytic system to remove sulfur and reduce it further down to less than 0,5% prior to passing through the centrifuge and the downstream pressure filtration unit in order to remove any residual water as well as any solid particles.

The DTPO is stored in bulk storage tanks in the tank farm and periodically transferred to smaller day tanks from which it is fed to the power generators to produce electricity. The light fraction oil is stored in a buffer tank for recycling to the oil burners of the waste incinerator for heating up the distillation furnace and/or the pyrolysis reactors. Similarly, the heavy fraction is also used in the same burners after diluting with light fraction as shown in the Process Flow Diagram, Fig.1 . The power generation process utilises standard ICE's (Internal Combustion Engines) for the production of electrical energy using the refined TPO as fuel. In the specific application described herein, two generator machines of capacity 8,9 MW each are used. All necessary auxiliary systems are included in the power plant, such as:

• Cooling Water Systems

· Lube oil systems

• Compressed air system

The invention comprises an innovative FG (Flue Gas) treatment section to ensure a thorough and adequate emission control system which, in this specific application, is based on the requirements of the applicable EU Directives (2010/75/eu on industrial emissions, 2015/2193/eu on the limitation of emissions of certain pollutants, 2008/98/eu on incineration of wastes as well as the applicable National Laws. It may be adapted to meet the requirements of the most stringest emission control limits applicable anywhere.

The system is also suitable to control the emissions of certain toxic pollutants such as dioxins and furans (PCDD/F's) etc. by the use of special gas incinerators with energy recovery systems whereby the temperature of the FG streams is raised to at least 850°C for a minimum residence time of 2 sec.

In this specific application of the invention the FG treatment system comprises 3 lines one for each of the two power generator machines and one to handle all FG emissions from the pyrolysis and distillation plants. Each line comprises 3 units in series, as shown in Fig.5, namely,

i) Incineration system operating at temperatures >850°C with energy recycling ii) Desulfurisation system (DSOx) for removal of the sulphur oxides down to less than the allowable limits

iii) Denitrogenisation system (DNOx) for removal of the nitrogen oxides down to less than the allowable limits

In the first line, the FG from the waste incinerator is firstly distributed to the various users (pyrolysis reactors and distillation plant) to provide energy for heating up the equipment and it is then directed to the FG treatment system comprising the DSOx (desulfurisation) and the DNOx (denitrogenisation) systems.

In each of the other 2 lines downstream the power generator machines, firstly the FG is passed through the incineration system (specially designed combustion chamber) via a preheater which raises the temperature to nearly that required. In the incinerator unit the temperature is maintained at 850°C for a minimum residence time of 2 seconds and it is then directed to the DSOx system.

The DSOx system of each line consists basically of an absorption tower where water is recirculated and a reaction tank as shown in Fig.6. Here slaked lime Ca(OH)2 is added to transform the oxides of sulphur (SOx) absorbed in the water into gypsum (CaS04) sludge which is filtered in a filter press and disposed off to other users in the form of bulk powder containing typically < 3% moisture as shown in the Process Flow Diagram, Fig. 6. The DSOx system also serves to retain the dust (PM). The FG exiting from the DSOx system is then passed through the DNOx system comprising an SCR (Selective Catalytic Reactor) unit in which urea solution is injected by means of a metering pump to transform the oxides of nitrogen (NOx) into gaseous nitrogen as shown in the Process Flow Diagram, Fig. 7.

From the DNOx system the treated FG is directed to the chimney for discharge to the atmosphere with any pollutants being well within the allowable limits. A continuous emissions monitoring system may be installed on the chimney to monitor and record the pollution parameters.

All processes comprising the invention are susceptible to full automation and control by systems such as PLC (Program Logic Control) or a DCS (Digital Control System) housed in the CCR (Central Control Room). BRIEF DESCRIPTION OF THE DRAWINGS

Fig.-1 illustrates, in the form of a block flow diagram, the overall process concept and shows ail processes comprising the overall concept of converting waste tyres into electricity and the co-products carbon-black (CB) and scrap steel.

Fig.-2 illustrates, in the form of a Process Flow Diagram, the pyrolysis section

Fig.-3/A illustrates, in the form of a Process Flow Diagram, an exemplary system of separating the scrap steel wires from the CB

Fig.-3/B illustrates, in the form of a Process Flow Diagram, an exemplary system for refining and upgrading the CB

Fig.-4 illustrates in the form of a Process Flow Diagram, the process of refining and upgrading the quality of TPO (Tyre Pyrolysis Oil) comprising distillation and other separation techniques

Fig. -5 illustrates in the form of a Block Flow Diagram, the overall system for treatment Of the FG (Flue Gas) comprising a unique gas incineration system, desulfurisation system (DSOx) and denitrogenisation system (DNOx).

Fig.-6 illustrates in the form of a Process Flow Diagram, the FG desulfurisation system (DSOx) and conversion of the sulphur oxides into gypsum

Fig,-7 illustrates in the form of a Process Flow Diagram, the FG denitrogenisation system (DNOx) utilising an SCR (Selective Catalytic Reactor) unit with urea solution injection

Claims

CLAIMS The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Overall concept of converting waste tyres into electricity by producing liquid fuel and upgrading it to make it suitable for combustion in ICE's (Internal Combustion Engines).

The concept of using a multiple number of pyrolysis reactors achieving economies of scale and smoothing out severe fluctuations in the whole process.

A system comprising a waste incinerator for burning any solid and/or liquid wastes and the non-condensable hydrocarbon gases supplying the energy of the FG (Flue Gas) leaving the incinerator to the pyrolysis reactors and the distillation unit.

The concept of refining the TPO (Tyre Pyrolysis Oil) by a system comprising distillation and other separation techniques to upgrade it to a quality standard suitable for combustion in ICE's (Internal Combustion Engines) for the generation of electrical power.

Unique system to treat the FG (Flue Gas) from the power generators to ensure that toxic pollutants such as dioxins/furans, if any, shall always be within allowable limits