IT201600100814A1 - Process and plant for the production of waste syngas, preferably industrial or municipal waste and related associated products. - Google Patents

Description

Process and plant for the production of syngas from waste, preferably industrial or municipal waste and related associated products

The present invention relates to a process and a plant for the production of a synthesis gas, or syngas, from waste, preferably industrial or urban waste and their derivatives.

More precisely, the invention relates to a process and a plant for producing synthesis gas which, when used as raw material for Fisher-Tropsch plants, methanol or ammonia, allows natural gas or other hydrocarbons to be replaced with waste or fuel from waste. (also known as RDF, which stands for refuse derived fuel).

As is known, population growth and the increase in wealth on a global basis have led to a dramatic increase in the amount of waste produced.

According to the known art, conventional waste management is aimed at minimizing the costs of collection and landfilling in favor of recycling and incineration, even if more and more waste materials are recycled (paper, some metals, etc. .).

New ideas are emerging to use waste or what is left of conventional recirculation as a new resource by recycling materials. The production of synthesis gas from waste by high temperature gasification is following in such a circular economy model.

This approach aims to save resources, mainly hydrocarbons, and minimize emissions and pollution, and consequently protect the environment also in terms of CO2 emissions.

A suitable gasification reactor must be designed for a conversion that complies with the requirements imposed on the composition of the synthesis gas to be used for a subsequent production of chemicals, requirements very different from the use of such synthesis gas as a fuel.

According to the known art, the reactors for gasification of waste or of fuel derived from waste as raw materials have in the past reached different degrees of efficiency and effectiveness, however the production of synthesis gas for the production of urea or methanol is still unused.

The main technical obstacles to be solved in order to have a correct design of this reactor are:

- the conversion of waste must be performed with O2 in order to have a high quality synthesis gas. A reactor based on the use of air cannot be used directly for the production of chemicals;

- the outlet temperature of the synthesis gas must be sufficiently high, 1050-1150 ° C, to avoid the reformation of harmful products and to limit the hydrocarbon content. The presence of hydrocarbons makes the downstream process more complex and requires a separate reforming step to convert these hydrocarbons into H2e CO;

- the temperature profile along the height of the reactor must be adequately controlled to avoid internal overheating and maintain a conversion efficiency above 99%;

- the temperature profile on the horizontal section of the reactor must be uniform in order to have a homogeneous conversion of the feed;

- the temperature of the slag in the lower part of the gasification reactor must be sufficiently high, 1400-1600 ° C, in order to keep the slag in a liquid phase with a carbon content lower than 1%;

- the reactor pressure must be slightly higher than atmospheric pressure to improve the safety of the plants;

- due to the high volume of synthesis gas required for chemical productions, the reactor design is preferably standardized for a specific capacity through a modular approach. Product capacity will be achieved by multiple reactors working in parallel.

In consideration of the above, it is evident the need for a process and a plant to produce a synthesis gas to be used for a subsequent production of chemical substances, starting from waste.

In this context, the solution according to the present invention is proposed, with the aim of providing a process and a plant for producing a synthesis gas that is suitable for use as raw material for Fischer-Tropsch plants, methanol, ammonia or urea, completely replacing the use of hydrocarbons.

Another object of the present invention is to minimize the emissions associated with the disposal of waste. Another object of the present invention is to recycle the waste carbon matrix into valuable products, such as urea, methanol, biofuels, by capturing the CO2 otherwise emitted by these plants.

Still another object of the present invention is to provide an economically efficient process for the production of chemicals.

A further object of the present invention is to provide a much cleaner and more uniform synthesis gas composition than current processes provide.

These and other results are obtained according to the present invention by proposing a gasification reactor with the following characteristics:

- waste feed flow located in an adequate vertical position, so as not to lower the temperature of the outgoing synthesis gas, but to obtain an adequate vertical temperature profile;

- multiple injection points for oxygen, to have adequate mixing with the raw material;

- multiple injection of a gaseous carrier, CO2 or H2O or raw gas to better control the temperature along the cross-sectional area and the height of the gasification reactor.

It is therefore an object of the present invention to provide a process and a plant for producing a synthesis gas from waste, preferably urban and / or industrial waste and their derivatives, allowing to overcome the limits of the solutions according to the known art and obtain the results technicians previously described.

A further purpose of the invention is that said process and plant for producing a synthesis gas from waste can be achieved with substantially limited costs, as regards both construction and operating costs.

Not the least object of the invention is to provide a process and a plant for producing a synthesis gas from waste that are substantially simple, safe and reliable.

Therefore, a first specific object of the present invention is a process for producing a synthesis gas from waste, preferably urban waste or fuel derived from waste, in which:

- the waste is fed into a reactor at a temperature between 20 and 800 ° C to form a fixed bed;

- oxygen is injected into the lower part of said fixed bed to react with said wastes in an oxidation reaction which gives a synthesis gas, the temperature of the bottom of said fixed bed being maintained in a range between 1400 and 2000 ° C, preferably between 1400 and 1600 ° C, to form a melting zone on the bottom of said fixed bed, in which the melting of the inert and metallic compounds contained in said waste is obtained;

- said synthesis gas flows through said fixed bed, causing an endothermic cracking reaction and a progressive lowering of the temperature, to form a gasification zone, until a temperature of about 800 ° C is reached in the upper part of said fixed bed;

- inside said reactor, oxygen is injected over said fixed bed, causing oxidation and increasing the temperature up to 1200 ° C, to form a post-heating area;

- a stabilization area is provided in the upper part of said reactor, in which the temperature is between 1050-1200 ° C;

and in which

- the temperature profile on the bottom and along the height of said reactor is controlled by injection of a flow of inert gas on the bottom of said fixed bed, together with oxygen.

Optionally, according to the present invention, natural gas is injected together with oxygen in the lower part of said fixed bed and / or above said fixed bed.

Preferably, according to the invention, oxygen is injected into a plurality of injection points.

In particular, always according to the present invention, said inert gas can be CO2.

A second specific object of the present invention is a plant for producing a synthesis gas from waste, preferably industrial or urban waste, according to the previously defined process, comprising a vertical cylindrical fixed bed reactor with a refractory inner lining and double steel walls with internal cooling water between the walls.

Preferably, according to the invention, a fixed bed of waste is provided inside said reactor, the height of said fixed bed being set at a level capable of reaching a temperature at the top of about 800 ° C.

In particular, according to the invention, said plant for producing a synthesis gas from waste comprises a plurality of O2 injection lances, said lances comprising two coaxial ducts, surrounded by a jacket for a cooling fluid.

A third specific object of the present invention is the use of synthesis gas produced according to the procedure defined above to produce hydrogen and CO2.

A fourth specific object of the present invention is the use of hydrogen produced according to the use of the synthesis gas previously defined to react together with nitrogen to produce ammonia.

A fifth specific object of the present invention is the use of ammonia produced according to the use of hydrogen previously defined to react with CO2 to produce urea.

Finally, a sixth specific object of the present invention is the use of synthesis gas produced according to the previously defined process for the production of methanol.

The invention will now be described below for illustrative but not limitative purposes, according to a preferred embodiment, with particular reference to the figures of the attached drawings, in which:

Figure 1A shows a schematic side sectional view of a reactor according to the present invention, together with the temperature profile along the reactor,

Figure 1B is a schematic plan and sectional view of the reactor of Figure 1A,

Figure 2 shows a sectional side schematic view of a particular portion of the reactor of Figures 1A and 1B, showing the temperature distribution in the fixed waste bed in the vicinity of an oxygen injection lance,

- figure 3 shows a schematic plan and sectional view of the reactor of figure 1A, together with the temperature profile in the lower part of the reactor before the control,

Figure 4 shows a sectional side schematic view of a particular portion of the reactor of Figures 1A and 1B, showing the temperature distribution in the fixed waste bed in proximity to an inert gas injection lance,

figure 5 shows a schematic plan and sectional view of the reactor of figure 1A, together with the temperature profile in the lower part of the reactor after the control, and

- Figure 6 shows a sectional side schematic view of the reactor of Figures 1A and 1B, together with a schematic view of the control architecture.

Referring to the figures, the process and the plant for producing synthesis gas from waste proposed according to the present invention, to obtain a synthesis gas suitable for the production of chemical substances must achieve the following objectives:

- avoid hydrocarbons, tars and compounds with high molecular weight in general,

- maximize the concentration of hydrogen and carbon monoxide,

- maximize the amount of hydrogen and carbon monoxide.

To achieve the first objective above, it is necessary to operate at high temperatures.

To obtain the necessary temperature level and to maximize the concentration of the important elements, i.e. hydrogen and carbon monoxide, in the synthesis gas, it is necessary to use pure oxygen as a gasification agent.

Finally, in order to maximize the quantity of hydrogen and carbon monoxide, it is advisable to select a charge with a high specific energy content (lower calorific value - PCI), typically containing a high quantity of non-recyclable plastics (such as PVC) and a low quantity. of water.

To implement this process, a cylindrical vertical type fixed bed reactor 10 is required. The reactor design has an internal 11 lining with special refractory and 12 double steel walls with 13 internal cooling water between the 12 walls (Jacket Cooling System) as a safety measure.

All the above operating conditions, pure oxygen and high PCI, could cause, under certain circumstances, temperatures higher than necessary and consequent greater wear of the refractory lining 11 of the reactor 10. In this case, a multiple injection of a gaseous carrier must be provided. , CO2or H2O.

Required temperature profile along the reactor Referring to Figure 1A, the required process temperature distribution is as follows. The temperature at the bottom 14 of the reactor 10 is 1600 ° C to obtain the melting process of the inert and metallic compounds inevitably present in the feed. A higher temperature is not necessary for most domestic and industrial waste and would only cause additional wear of the refractory.

The hot smoke generated by the partial oxidation that occurs in the lower part of the reactor 10 flows through the fixed bed 14, causing the endothermic cracking reaction typical of gasification, and a cooling. The height of the bed 14 is set at an adequate level to obtain a temperature at the top of about 800 ° C, the minimum temperature necessary for or carrying out most of the gasification process.

Upon exiting the fixed bed 14, a fraction of the synthesis gas is burned with oxygen to reach a temperature above 1100 ° C and thus complete the conversion of more resistant compounds such as naphthalenes and paraffins.

The ideal horizontal temperature distribution must be uniform. To get as close as possible to this objective, oxygen is injected into the reactor 10 through a series of lances 15 arranged radially as shown in Figure 1B.

Inside the gasification reactor 10 different areas can be identified (starting from the bottom of the reactor):

- a melting zone 16, at a temperature ranging from 1400 to 1600 ° C,

- a gasification zone 17 at a temperature ranging from 800 to 1600 ° C,

- a post-heating zone 18 at a temperature ranging from 800 to 1200 ° C,

- a stabilization zone 19 at a temperature ranging from 1050 to 1250 ° C.

Real temperature distribution

The quantity of oxygen injected into the lower part of the reactor 10 is related to the composition of the waste and controls the productivity of the system. In fact, the process temperature profile is a not so controllable result by the amount of oxygen.

In case of a temperature at the bottom of the reactor 10 below 1600 ° C, resulting from a charge with low PCI, a certain amount of natural gas can be injected through a second channel 20 of the oxygen lances 15. This channel is also used for the heating of the reactor and a minimum flow rate must be maintained in any case to protect against a clogging caused by the molten inert (purge gas).

The oxygen injected by the lances 15 impacts the material that forms the bed 14 and, despite the high speed, is partially pushed back. It reacts violently in the vicinity of the refractory 11, especially in the presence of natural gas. As shown in Figure 2, this causes an uneven temperature distribution, with overheated areas on the refractory lining 11 around the heads of the lances 15, where the temperature can easily exceed 2000 ° C. This effect is aggravated by material with high PCI which causes a general increase in temperatures at the bottom of the reactor 10 and in general a bed 14 which is more compact and difficult to penetrate. The resulting temperature profile in the cross section of the reactor 10 is shown in Figure 3.

Use of inert gas to control temperature

To reduce unwanted overheating, while preserving the efficiency of the reactor 10, an inert gas flow can be used. A small amount of room temperature inert gas is introduced at a low rate in place of the natural purge gas, which creates a cushion around the heads of the lances to decrease the local temperature.

In the case of material with high PCI, the amount of inert gas can be increased to create a larger cooling effect to stabilize the temperature profile.

In the case of chemical application of synthesis gas (such as for the production of urea) a certain amount of CO2 is usually available as a by-product. The use of this inert gas is generally preferable in order not to alter too much the chemical species present at the outlet in the synthesis gas. Alternatively, if possible, nitrogen can be used.

The resulting cross-sectional profile is shown in Figures 4 and 5.

Table 1 shows the effect of CO2 injection in the case of high calorific value waste.

Case 1 represents the condition without the flow of aggregates, Case 2 with low quantity of CO2 (shock-absorbing effect only), Case 3 with an established quantity of CO2 to reduce the background temperature calculated for the required working condition. Table 1

Effect of CO2 injection flow on synthesis gas composition

U.M. Case 1 Case 2 Case 3 Waste Inlet t / h 10.0 10.0 10.0 Waste PCI MJ / kg 20.97 20.97 20.97 CO2 InletNm <3> / h 0 330 2000 O2 Inlet side

Nm <3> / h 3 380 3380 3380 lower

O2 post-Nm input <3> / h 650 650 750

heating

Average side temperature

1992 1922 1606 ° C lower

H2% vol 42.27 40.85 33.86 CO% vol 44.73 45.26 47.14 CO2% vol 8.28 9.18 14.29 synthesis gas flow Nm <3> / h 16858 16757 17568 PCI synthesis gas MJ / Nm <3> 10.14 10.05 9.52

As shown in Table 1, the injection of small quantities of inert gas does not significantly change the quantity and quality of the synthesis gas, while the increase in the flow of CO2 significantly changes the balance of CO / CO2 / H2 in the synthesis gas produced. .

If we evaluate the H2 / CO2 ratio after the water gas shift this ratio moves from 1.64 to 1.32 for Case 3.

Control strategy

In order to control and maintain the correct cross-sectional temperature and distribution profile in the lower and upper part of the reactor, the following control philosophy is adopted as shown in figure 6.

The control of the bottom temperature of the reactor is carried out by means of a computerized system (fuzzy logic) which takes into consideration the following parameters:

- type of waste,

- productivity,

- background temperature by thermal camera (TV),

- refractory temperature (T1),

- intermediate temperature (T2),

- operator settings.

The system regulates the injection flows of natural gas or inert gas by means of motorized valves.

The operator can select whether to activate or deactivate the system and the intervention force (protection of the wall or reduction of the process temperature).

The temperature control of the upper part of the reactor is carried out by means of a computerized PID (Proportional Integral Derivative) controller which takes into account the following parameters:

- upper side temperature (T3),

- intermediate temperature (T2),

- hydrogen content,

- operator setting.

The system acts on the injection of natural gas and oxygen by means of motorized valves.

The operator can select whether to use only the combustion of synthesis gas to increase the temperature or to inject natural gas.

This second option is used in case of need to preserve the hydrogen content of the synthesis gas, especially in the case of charge with low PCI.

The present invention has been described for illustrative, non-limiting purposes, according to a preferred embodiment, but it must be understood that variations and / or modifications can be made by those skilled in the art without thereby departing from the relative scope of protection, as defined by claims attached.

Claims (11)

CLAIMS 1) Process for producing a synthesis gas from waste, preferably urban waste or fuel derived from waste, in which: - the waste is fed into a reactor at a temperature between 20 and 800 ° C to form a fixed bed; - oxygen is injected into the lower part of said fixed bed to react with said wastes in an oxidation reaction to give a synthesis gas, the temperature of the bottom of said fixed bed being maintained in a range between 1400 and 2000 ° C, preferably between 1400 and 1600 ° C, to form a melting zone on the lower part of said fixed bed, in which the melting of the inert and metallic compounds contained in said waste is obtained; - said synthesis gas flows through said fixed bed, causing an endothermic cracking reaction and a progressive lowering of the temperature, to form a gasification zone, until a temperature of about 800 ° C is reached in the upper part of said fixed bed; - oxygen is injected into said reactor, above said fixed bed, causing oxidation and increasing the temperature up to 1200 ° C, to form a post-heating area; - a stabilization area is provided in the upper part of said reactor, where the temperature is between 1050-1200 ° C; and in which - the temperature profile at the bottom and along the height of said reactor is controlled by injecting a flow of inert gas into the lower part of said fixed bed, together with oxygen. 2) Process for producing a synthesis gas from waste according to claim 1, characterized in that natural gas is injected together with oxygen, in the lower part of said fixed bed and / or above said fixed bed. 3) Process for producing a synthesis gas from waste according to claim 1 or 2, characterized in that oxygen is injected into a plurality of injection points. 4) Process for producing a synthesis gas from waste according to any one of the preceding claims, characterized in that said inert gas is CO2. 5) Plant for producing a synthesis gas from waste, preferably industrial or urban waste, according to the process of any one of claims 1 - 4, characterized in that it comprises a fixed-bed reactor (10) of the cylindrical vertical type, with a internal lining (11) with refractory and double steel walls (12) with internal cooling water (13) between the walls (12). 6) Plant for producing a synthesis gas from waste according to claim 5, characterized in that a fixed bed (14) is provided inside said reactor, the height of said fixed bed (14) being fixed to a level able to reach a temperature at its top of about 800 ° C. 7) Plant for producing a synthesis gas from waste according to claim 5 or 6, characterized in that it comprises a plurality of O2 injection lances, said lances comprising two coaxial ducts, surrounded by a jacket for a cooling fluid. 8) Use of synthesis gas produced according to claims 1 - 4 to produce hydrogen and CO2. 9) Use of hydrogen produced according to claim 8 to react together with nitrogen to produce ammonia. 10) Use of ammonia produced according to claim 9 to react with CO2 to produce urea. 11) Use of synthesis gas produced according to claims 1 - 4 to produce methanol.