PROCESS FOR OBTAINING SYNTHESIS GAS EITHER FROM SOLID FUELS DERIVED FROM URBAN SOLID WASTE, OR FROM INDUSTRIAL SOLID WASTE

Abstract: A process is disclosed, by means of which synthesis gas can be obtained either from solid fuels derived from urban solid waste (RDF), or from industrial solid waste, characterized in that said solid fuels (RDF) or said industrial solid waste are gasified with essentially pure oxygen under a pressure comprised within the range of from 1 to 100 abs.atm, by co-currently feeding said reactants to a gasifier as adiabatic as possible, and that the gas leaving the gasifier is treated in order to remove the polluting, acidic gases, by means of a washing step.

Description: The present invention relates to a process for obtaining synthesis gas either from the solid fuels derived from urban solid waste, or from industrial solid waste. The solid fuels derived from the urban solid waste (commonly denominated as "RDF", or, in Italy, as "CsdR"), are the lightest, combustible fraction of the urban solid waste, i.e., they are constituted by plastics, paper, wood, and textile materials (with the possible presence of organic matter). said fuels have a net heat value comprised within the range of from 10450 kJ/kg to 18850 kJ/kg (2,500 to 4,500 kcal/kg), according to the separation degree, as well as to their moisture content. A general scheme of the process for producing said RDF comprises the following operations: trituration of the urban solid waste; magnetic separation; air sorting in order to separate the light fractions from the heavy fractions; drying of the light material; possible pelletizing of the resulting product. Among the many factors of differentiation of RDF, besides the composition of the urban solid waste used as the starting material, there is the technology used in order to select the derived fuel. The use of said RDF is for being burnt in boilers, and, above all, in cement factories. The present Applicant has found now that said RDF or said solid industrial waste can be gasified under suitable conditions, in order to obtain synthesis gas. The present invention, therefore, provides a process for gassifying the combustible fraction of municipal- or industrial solid waste to produce synthesis gas by gassification with a pressurized oxygen-containing gas at a minimum temperature of 1000°C, characterized by comprising the steps of: cocurrently feeding said combustible fraction and technically pure oxygen pressurized at a pressure of from 0,1 MPa to 10 Mpa (1 abs.atm to 100 abs.atm) to an adiabatic gassifier, and washing the as-produced synthesis gas to remove the acidic gaseous components. Both in case of RDF, and in case of industrial solid waste, it is recommended that they should have a net heat value of a least 12560 kJ/kg (3,000 kcal/kg), and a moisture content lower than, or at maximum equal to, 30%. Among the industrial solid waste which an be used, the exhausted tyres can be mentioned in particular; anyway, also other types of industrial waste can be selected. As regards the gasification pressure, the preferred range if of from 1,5 MPa to 5 MPa (15 to 50 abs.atm) in case RDF are used, and of from 0,1 MPa to 5 MPa (1 to 50 abs.atm) in case industrial solid waste is used. The temperature of the gasifier is defined both as a function of the moisture content of RDF or of the industrial waste, and of their heat value, and as a function of the amount and of the temperature of the oxygen fed to the process. Oxygen, before being fed to the gasifier, can be pre-heated at a temperature equal to, or higher than, the temperature-of the same gasifier. Said oxygen can be produced, e.g., in an air fractionating facility, or in an equivalent facility. In such case, using a portion of the synthesis gas obtained (such as, e.g., about 10%), in order to have the necessary power for managing said air fractionating facility, or an equivalent facility, can be advantageous. The treatment of the gas leaving the gasifier in order to remove the acidic gases can be carried out, e.g., by means of a washing step with sodium hydroxide. Furthermore, cooling the gas leaving the gasifier before such a treatment is carried out, can be advantageous. Some examples are given now in order to better illustrate the invention without limiting it. Example 1 A solid fuel derived from urban solid waste (RDF) was used, which had a net heat value of 16330 kJ/kg (3,900 kcal/kg), and contained 22.4% of moisture. The gasification was carried out in a gasifier as adiabatic as possible, with 104 kg/hour of RDF and 48 kg/hour of essentially pure oxygen being co-currently fed to the process, under the following conditions: P = 5 MPa (50 abs.atm); average T = 1,000°C After the washing, 163 Nm³/hour of synthesis gas was obtained, which had a net heat value of 12430 kJ/Nm³ (2,969 kcal/Nm³), as referred to dry gas. A stream of 17 Nm³/hour was diverted from the produced stream of 163 Nm³/hour of gas in order to generate the necessary electric power for operating the air fractionating facility. Example 2 Exhausted tyres were used as the industrial solid waste, which had a net heat value of 25100 kJ/kg (6,000 kcal/kg) and showed an accidental moisture content of 15%. The gasification was carried out in a gasifier as adiabatic as possible, with 102 kg/hour of exhausted tyres and 69 kg/hour of essentially pure oxygen being co-currently fed to the process, under the following conditions: P = 0,1 MPa(1 abs.atm); average T = 1,200°C After the washing, 195 Nm³/hour of synthesis gas was obtained, which had a net heat value of 11820 kJ/Nm³ (2,824 kcal/Nm³), as referred to dry gas. A stream of 25 Nm³/hour was diverted from the produced stream of 195 Nm³/hour of gas in order to generate the necessary electric power for the operations of the air fractionating facility. Example 3 A solid fuel deriving from urban solid waste (RDF) was used, which had a net heat value of 16540 kJ/kg (3,950 kcal/kg), and contained 7% of moisture. The gasification was carried out in a gasifier as adiabatic as possible, with 127 kg/hour of RDF and 47 kg/hour of essentially pure oxygen being co-currently fed to the process, under the following conditions: P = 1,5 MPa (15 abs.atm); average T = 1,220° C After the washing, 162 Nm³/hour of synthesis gas was obtained, which had a net value of 10870 kJ/Nm³ (2,596 kcal/Nm³), as referred to dry gas. A stream of 19 Nm³/hour was diverted from the produced stream of 162 Nm³/hour of gas in order to generate the necessary electric power for operating the air fractionating facility.

Claims: Process for gassifying the combustible fraction of municipal- or industrial solid waste to produce synthesis gas by gassification with a pressurized oxygen-containing gas at a minimum temperature of 1000°C, characterized by comprising the steps of: cocurrently feeding said combustible fraction and technically pure oxygen pressurized at a pressure of from 0,1 MPa to 10 Mpa (1 abs.atm to 100 abs.atm) to an adiabatic gassifier, and washing the as-produced synthesis gas to remove the acidic gaseous components. Process according to Claim 1, wherein the pressure of the technically pure oxygen is from 1,5 MPa to 5MPa (15 abs.atm to 50 abs.atm). Process according to Claim 1, wherein the combustible fraction of industrial solid waste is gassified under an oxygen pressure of from 0,1 MPa to 5 MPa (1 abs.atm to 50 abs.atm). Process according to Claim 1, wherein the oxygen feedstock is preheated at a minimum temperature equal to the temperature obtaining in the adiabatic gassifier. Process according to Claim 1, wherein said combustible fraction has a minimum net heating value of 12560 kJ/kg (3000 kcal/kg) and a maximum moisture content of 30% by weight. Process according to Claim 1, wherein the industrial waste solid combustible fraction derives from used tyres.

Inventors: CARVANI, LUIGI, GARUTI, GIULIANO
Applicants: ENIRICERCHE S.P.A.
Application year: 1990
Main classification: C10J3
IPC codes: C10J3