JPH0448518B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Background of the Invention Hydrocarbon oils derived from petroleum and similar sources contain varying amounts of nitrogen and sulfur compounds. Removal of such compounds during the refining process of the oil because they impart undesirable properties to marketable products such as unpleasant odors, corrosivity, bad color, and increased release of pollutants. is often desirable. Additionally, these compounds have an adverse effect on various refining processes that use catalysts applied to oil; nitrogen compounds can deactivate some hydrocracking catalysts and remove excess gas and coke in the cracking process. It tends to cause generation. Various techniques have been devised to remove nitrogen and sulfur from oil, but perhaps the most common and most suitable method is nitrogen removal, usually promoted by elevated temperature and pressure and a hydrogenation catalyst. and hydrorefining using catalysts that convert sulfur to NH ₃ and H ₂ S by reacting with hydrogen. Similar reactions in which nitrogen and sulfur compounds are reacted with hydrogen to form NH ₃ and H ₂ S include thermal cracking, catalytic cracking, reforming and hydrogenation processes not specifically designed for this purpose. It also occurs in other methods such as hydrocracking. Therefore, there are various reaction effluents containing NH ₃ and H ₂ S produced in this way.

Removal of NH ₃ and H ₂ S from such hydrocarbon reaction effluents may be accomplished by scrubbing with water, preferably at elevated pressure and low temperature. However, in order to achieve the desired degree of removal, large amounts of water often have to be used so that a dilute aqueous solution of _NH3 and _H2S (1-10% by weight _NH4HS ) is formed. . In order for this water to be discharged under NPDES authorization, this acidic water is generally converted into _NH3 and _H2S .
must be removed.

One typical prior art process involves the separate recovery of ammonia and hydrogen sulfide from such wastewater by stripping distillation carried out at superpressure in connected distillation columns. Hydrogen sulfide vapor is removed as overhead from one column (hydrogen sulfide stripper) and the bottoms from that column are passed to another column (ammonia stripper) where a portion of the overhead vapor is removed. Ammonia vapor is recovered by condensation and a portion of the condensate is recycled to the first column. Purified water is withdrawn as bottoms from the second column. This method works well for removing ammonia and hydrogen sulfide from petroleum-derived effluent streams when the weight ratio of NH ₃ to H ₂ S is typically 0.5; At high effluents (such as effluent streams derived from Sier oil), ammonia levels in the hydrogen sulfide stripper column due to ammonia in the recycled condensate are further increased. This means that NH ₃ vs.
The _H2S ratio is further increased until _H2S removal in the _H2S stripper column becomes difficult, and the _H2S in the feed for certain _NH3 : _H2S ratios is
becomes impossible to remove.

SUMMARY OF THE INVENTION The present invention overcomes the deficiencies of the prior art by having an ammonia stripper precede a hydrogen sulfide stripper. This system reduces the amount of ammonia in the hydrogen sulfide stripper feed by removing some of the ammonia overhead in the ammonia stripper but leaving essentially all the hydrogen sulfide. In this method, wastewater is stripped in an ammonia stripper with an overhead vapor of water and hydrogen sulfide, the ammonia is extracted from the ammonia stripper, and a bottom liquid of stripped water is added to the ammonia stripper. removed from par. A portion of the overhead vapor condenses to form a non-condensable portion consisting of substantially hydrogen sulfide and water-free ammonia vapor and a condensed portion consisting of water, hydrogen sulfide and ammonia.
A portion of the condensate is returned to the ammonia stripper and the remainder of the condensate is diluted with a portion of the stripped water to reduce the ammonia concentration in the condensate portion to less than 10 wt%. This diluted condensate portion forms a thermal updraft vapor in the hydrogen sulfide stripper and countercurrently contacts the relatively cold liquid water descending through the stripper. The bottom of the hydrogen sulfide stripper is 320~390〓
It is operated at a temperature of Overhead vapor consisting essentially of ammonia-free hydrogen sulfide is withdrawn from the hydrogen sulfide stripper. A bottoms liquid consisting of water, hydrogen sulfide and ammonia is also removed from the hydrogen sulfide stripper and recycled to the ammonia stripper.

The bottom of the ammonia stripper is preferably
Operated at temperatures of 300-320㎓ and pressures of 50-80 psig. The stripped water can be used to heat the wastewater and the diluted condensate fraction can be heated to its bubble point before being stripped in a hydrogen sulfide stripper. Preferably, the diluted condensate portion is provided at a point where the composition of the stripper's internal liquid matches the composition of the diluted condensate portion. Preferably, a side stream is removed from the hydrogen sulfide stripper, the side stream is cooled, and the cooled side stream is recycled to the hydrogen sulfide stripper.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In its broadest application, the present invention includes a method for separating hydrogen sulfide and ammonia from wastewater having an ammonia to hydrogen sulfide ratio of at least 4:1, wherein the ammonia stripper is combined with the hydrogen sulfide stripper. Prior to this, the feed to the hydrogen sulfide stripper was diluted to an ammonia concentration of less than 10 wt%, and the bottom of the hydrogen sulfide stripper was
Operated at temperatures of ~390㎓. The term "stripping" is used herein to pass hot vapor or gas generated or introduced at the bottom of a multistage contacting column upwardly in a downflow, thereby reducing the used to characterize the decrease in the concentration of the most volatile components in that liquid. A distillation zone consists of one or more columns and the accessories typically associated therewith.

The operation of the method will now be explained with reference to the drawings which show preferred embodiments of the invention. In this aspect,
passing wastewater at 114㎓ containing 4.9% ammonia and 0.7% hydrogen sulfide (6.9:1 weight ratio of ammonia to hydrogen sulfide) through a feed/bottoms heat exchanger 10 and heating the wastewater to 260㎓; then adding recycled wastewater containing 7.2% ammonia and 1.2% hydrogen sulfide to this wastewater;
A wastewater feed containing 5.8% ammonia and 0.9% hydrogen sulfide (6.4:1 weight ratio of ammonia to hydrogen sulfide) is formed at 295㎓. This wastewater is fed to an ammonia stripper 20, where the ammonia is stripped. Bottom liquid is 309
and 77 psia. This liquid is stripped wastewater containing less than 0.006 ammonia and hydrogen sulfide. Overhead steam is removed from the ammonia stripper 20 at 244㎓ and 69 psia. This overhead vapor containing water, hydrogen sulfide and ammonia enters an ammonia stripper overhead condenser 30 and an ammonia stripper reflux drum 40.
and partially condensed at 120〓 and 65 psia. The uncondensed portion consists of substantially hydrogen sulfide and water-free ammonia vapor (95.9% ammonia in this embodiment). These uncondensed vapors may be further purified and compressed to produce anhydrous ammonia products. Its condensate part consists of 46.1% ammonia, 38.5% water and 15.4% hydrogen sulfide. Some of this condensation is returned to the ammonia stripper 20.
Approximately 67% of the stripped water, consisting of net stripped water, passes through a feed/bottoms heat exchanger to heat the wastewater, and the remaining stripped water is returned to the ammonia stripper. is added to the condensate portion of the free overhead vapor to dilute the condensate portion such that the diluted condensate portion contains 7.5% ammonia and 2.5% hydrogen sulfide. This diluted condensate part is 10wt
%, higher ammonia concentrations adversely affect the ammonia/hydrogen sulfide balance in the hydrogen sulfide stripper. This diluted condensed portion passes through a preheater 50 where this diluted condensed portion is
320° and then fed to the lower portion of the hydrogen sulfide stripper at a point where the composition of the dilute condensate portion is commensurate with the composition of the internal liquid of the hydrogen sulfide stripper. This hydrogen sulfide stripper 60
Therein, the diluted condensate section is stripped to form a heated vapor which is contacted countercurrently therein with a cooler downward flowing liquid. These liquids are produced by cooler circulation pumps. In the upper part of this tower, the heat rising steam is
It is scrubbed by a countercurrent flow of a relatively cool liquid water stream formed by introducing 100 ml of condensate at the top of the hydrogen sulfide stripper. Overhead steam consisting essentially of hydrogen sulfide without ammonia is 100〓,
It is extracted from a hydrogen sulfide stripper at 248 psia. This hydrogen sulfide vapor stream may be fed to a Claus sulfur plant for sulfur recovery. 91.4% water, 7.2% ammonia and
The bottom liquid consisting of 1.2% hydrogen sulfide is 355〓,
The bottoms liquid withdrawn from the hydrogen sulfide stripper 60 at 250 psia. is recycled to the ammonia stripper by adding the bottoms liquid to the wastewater feed to form the ammonia stripper 20 feed.

Preferably, the bottom of the ammonia stripper is operated at a temperature of 300-320° and a pressure of 50-80 psig.

Although the invention has been described in terms of specific embodiments,
This application is intended to cover modifications and alterations that may be made by those skilled in the art without departing from the scope and spirit of the appended claims.

[Brief explanation of the drawing]

In order to better understand the invention, reference is made to the drawings of preferred embodiments of the invention. The drawings are for illustrative purposes only and should not be construed as limiting the invention. This drawing is a process diagram of a preferred embodiment of the present invention.

Claims (1)

Claims: 1. A method for separating hydrogen sulfide and ammonia from wastewater in which the weight ratio of ammonia to hydrogen sulfide is at least 4:1, comprising: (a) stripping said wastewater in an ammonia stripper; b) withdrawing overhead vapor from the ammonia stripper, said vapor comprising water, hydrogen sulphide and ammonia; and (c) extracting from the ammonia stripper a bottom liquid consisting of stripped water. (d) partially condensing said overhead vapor to form an uncondensed portion consisting essentially of hydrogen sulfide and water-free ammonia vapor and a condensed portion consisting of water, hydrogen sulfide and ammonia; (e) returning some of said condensed portion to said ammonia stripper; (f) adding some of said stripped water to the remainder of said condensed portion; diluting the ammonia concentration to less than 10 wt%; (g) stripping the diluted condensate in a hydrogen sulfide stripper;
Attach the bottom of the hydrogen sulfide stripper to 320°~
(h) extracting overhead vapor from the hydrogen sulfide stripper, wherein said vapor consists essentially of ammonia-free hydrogen sulfide; withdrawing a liquid, said liquid comprising water, hydrogen sulfide and ammonia, and (j) recycling said bottom liquid from said hydrogen sulfide stripper to said ammonia stripper; The method for separating hydrogen sulfide and ammonia from wastewater, characterized in that: 2. Attach the bottom of the ammonia stripper to 300~
A process for separating hydrogen sulfide and ammonia from wastewater according to paragraph 1, wherein the ammonia to hydrogen sulfide weight ratio is at least 4:1, operating at a temperature of 320㎓ and a pressure of 50 to 80 psig. 3. wherein said stripped water is used to heat said wastewater, wherein the weight ratio of ammonia to hydrogen sulfide is at least 4:1.
A method for separating hydrogen sulfide and ammonia from wastewater. 4. The diluted condensate fraction is heated to at least its bubbling point before being stripped in the hydrogen sulfide stripper, wherein the ammonia to hydrogen sulfide weight ratio is at least 4:1. Method for separating hydrogen sulfide and ammonia from wastewater. 5. Supplying said diluted condensate portion in step (f) to said hydrogen sulfide stripper at a time when the composition of the internal liquid of said stripper is compatible with the composition of said diluted condensate portion. A method for separating hydrogen sulfide and ammonia from wastewater as described, wherein the weight ratio of ammonia to hydrogen sulfide is at least 4:1. 6. Ammonia vs. sulfide according to paragraph 1, wherein said side stream is withdrawn from said hydrogen sulfide stripper, said side stream is cooled, and said cooled side stream is recycled to said hydrogen sulfide stripper. A method for separating hydrogen sulfide and ammonia from wastewater, wherein the hydrogen weight ratio is at least 4:1.