PROCESS FOR REDUCING CORROSIVE CONTAMINANTS IN PROCESS WATER

Abstract

The disclosure relates to a process for the reduction of corrosive contaminants in process water, mainly through air or oxygen-containing gas or even pure oxygen injection into the riser, converting part of the ammonia carried from the regenerator to the riser into N.sub.2, and reducing the ammonia and cyanide content in the process water condensed in the product recovery section.

Claims

1. A process for a reduction of corrosive contaminants in process water, the process comprising: injecting feedstock into a feedstock injection nozzle located 4 m above a base of a riser; injecting air or oxygen-containing gas or even pure oxygen into the base of the riser through a lift steam injection nozzle below the feedstock injection nozzle; and using a combustion promoter to a catalyst.

2. The process of claim 1, wherein the combustion promoter to the catalyst is selected from platinum, palladium, rhodium, and iridium.

3. The process of claim 2, wherein the combustion promoter has a maximum noble metal content in the catalyst inventory equivalent to 1 ppm on a mass basis in the catalyst.

4. A process for a reduction of corrosive contaminants in process water, the process comprising: injecting feedstock into a feedstock injection nozzle located 4 m above a base of a riser; injecting air or oxygen into a specific nozzle below the feedstock injection nozzle; and using a combustion promoter to a catalyst.

5. The process of claim 4, wherein the combustion promoter to the catalyst is selected from platinum, palladium, rhodium, and iridium.

6. The process of claim 5, wherein the combustion promoter has a maximum noble metal content in the catalyst inventory equivalent to 1 ppm on a mass basis in the catalyst.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0016] FIG. 1 illustrates the feedstock injection nozzle (100), the lift steam injection (200) and the air or oxygen injection (300) according to an embodiment of the disclosure.

[0017] FIG. 2 shows the process flowchart of the fluid catalytic cracking process including the application of the disclosure to the control of corrosion precursors in the product recovery section.

DETAILED DESCRIPTION

[0018] Embodiments of the present disclosure refer to a process for reducing corrosive contaminants in process water comprising the following steps: [0019] (a) Injection of feedstock through a feedstock injection nozzle (3) located 4 m above the steam injection nozzle at the base of the riser (100); [0020] (b) Injection of air or oxygen-containing gas or even pure oxygen into the base of the riser through the lift steam injection nozzle (4) below the feedstock injection nozzle (3) or by specific injection nozzle; and [0021] (c) Use of combustion promoter with maximum noble metal content in the catalyst inventory equivalent to 1 ppm in the catalyst along with the injection of air or oxygen-containing gas or pure oxygen.

[0022] For a better understanding of the mechanism of action of the disclosure, it is convenient to know the flowchart of a fluid catalytic cracking process, as exemplified in FIG. 2. A preheated feedstock (1) is injected into a riser (2) through a feedstock injector nozzle (3), coming into contact with hot regenerated catalyst from a regenerator (13). Feedstock vaporization and volumetric expansion propel the catalyst and vaporized products to the top of the riser and into a separator vessel (6), where the spent catalyst, deactivated by the coke produced, and the volatile products are separated.

[0023] The volatile products (or cracking products) (7) are routed to the product recovery section and the spent catalyst to a stripper (9) where residual volatile products retained in the catalyst pores are recovered by steam injection. From the stripper (9), the spent catalyst is transferred to a regenerator (10) via a transfer line (8). In the regenerator (10), the coke from the spent catalyst, containing a relatively low content of nitrogen compounds from the feedstock, is burned with air (11) to produce combustion gas (12). The combustion regime can be total or partial. In the latter, due to the scarcity of oxygen, a larger portion of the nitrogen in the coke is converted into reduced species: ammonia and HCN. After the regeneration step, the regenerated catalyst is transferred back to the riser through a transfer line (13). A small portion of the combustion gas, including nitrogen species, is carried along with the regenerated catalyst.

[0024] At the base of the riser (2), fluidization steam (4) is injected to raise the catalyst to the topmost charge injection point. Along with the fluidization steam, air or oxygen-containing gas or even pure oxygen is injected through the injection nozzle (5) object of the invention, as shown in FIG. 1. The injection of air at the base of the riser converts the reduced nitrogen species from the regenerator to N.sub.2 and NOx, which are inert to the corrosive process of the cold area.

[0025] The cracking products (7) exiting the top of the separator vessel proceed to a main fractionator (14) where they are cooled by circulating refluxes from the lateral withdrawals of a tower (16), with the lightest product of all being withdrawn from a top (15) of the tower (16), where it is partially condensed and collected in a top drum (17), which separates a light naphtha (18), gases (19), and part of a condensed water vapor (20).

[0026] The gases, in turn, proceed to a gas recovery section (21), where they go through the two stages of compression for LPG condensation. Wash water is injected into the discharge of a first compression stage (22). The condensed liquid streams and the gas streams are sent to a high-pressure vessel (23). At the high-pressure vessel (23), the streams are separated into a the mixture of light naphtha and LPG (24) that sent to the distillation and fractionation section, non-condensed gases (25) which go to the absorber, and a second part of the process water (26), in which the reduced nitrogen species that accelerate the corrosive process are dissolved.

Example

[0027] The proposed process was tested in a prototype research unit of a circulating FCC, with 200 kg/h of feedstock flow and 350 kg of catalyst inventory, equipped with a riser of 18 m in length.

[0028] The unit was operated in partial combustion, with the CO.sub.2/CO ratio of the combustion gas being equal to 3. The unit operated with a used refinery catalyst without a combustion promoter and with a vacuum gasoil feedstock.

[0029] The temperature of the riser was 535 C. and the temperature of the regenerator was 680 C.

[0030] Thus, the air flow rate injected in the example was 1 kg/h. The calculation of the air flow rate was made by the CO content in the combustion gas multiplied by the inert gas content carried from the regenerator to the reactor. The air injection in tests following the example cited was varied from 0.5 kg/h to 2 kg/h. The air flow rate was proportional to the vacuum gasoil feedstock flow rate of 200 kg/h.

[0031] Additionally, four conditions were compared: in the first, the base case, 1 kg/h of nitrogen was injected at the base of the riser; in the second condition, 1 kg/h of air was injected; the third condition repeated the air injection and added 20 g of a platinum-based commercial combustion promoter to the 350 kg of the base catalyst; and in the fourth condition, the unit was operated in complete combustion with 3% excess O.sub.2 in the combustion gas. To date, the best condition tested was the one in which the injection was combined with the use of the combustion promoter in the catalyst, whose maximum platinum or noble metal content is equivalent to 1 ppm in the catalytic system. Other metals can be used as combustion promoters in the catalyst, like palladium, rhodium and iridium.

[0032] The process water was sampled in the water/oil separation vessel at a pressure of 1.6 kgf/cm.sup.2 g and the ammonia content in the water was measured using the APHA 4500(SM4500NH3) method. The ammonia nitrogen contents measured in the first three conditions were respectively 2,992 mg/kg, 2,304 mg/kg, 1,695 mg/kg and 1,400 mg/kg. The injection of air into the riser reduced the ammonia nitrogen content by 700 mg/kg and the air injection combined with the combustion promoter reduced the ammonia nitrogen by 1,300 mg/kg compared to the base case.

[0033] In the example, air was injected into the base of the riser through the double-fluid lift steam injection nozzle (100), shown in FIG. 1, and the feedstock was injected into a nozzle located 4 m above the base of the riser, ensuring a residence time of up to 4 s for the reaction of the ammonia from the regenerator with the oxygen from the injected air before the upflow reached the feedstock.

Application

[0034] Embodiments of the disclosure reduce the concentration of nitrogen species in the process water from FCC units operating in partial combustion, and thus reduce the corrosion rates of equipment in the product recovery section, extending the service life of the equipment and reducing operational risks.

[0035] Embodiments of the disclosure extend the service life of the equipment in the UFCC gas recovery section, which does not need to be changed as frequently, avoiding the associated costs.

[0036] This reduces the incidence of cracks in the equipment of the gas recovery section, thus reducing the risks of hydrocarbon leaks to the outside.

[0037] By reducing the corrosion rate, the reliability of the equipment in the FCC gas recovery section is increased.