SE524106C2 - Purification of condensate from evaporator and cooker in sulfate pulping process, comprises addition of acidifying agent to methanol column used to remove ammonia - Google Patents

Abstract

An acidifying agent is added to the methanol column (17) used to remove ammonia from the condensate (1). A method for preparing sulfate pulp includes steps for reducing nitrogen oxide (NOx) emissions and obtaining a flow of ammonia-rich liquid by using a stripper (15) and a methanol column to purify the condensate, which generates a volatile methanol fraction. An acidifying agent is added to the methanol column.

Description

20 25 30 35 524 106 A much better solution is to lower the pH of the methanol column and instead enrich the ammonia in the bottom product from the methanol column. This current is easier to handle because the feed is only a fraction of it out of the stripper. The feed from the methanol column is about 1% of the feed from the stripper. Ammonia can thereby be obtained in a much higher concentration, which facilitates further handling.

The invention will now be further described below with reference to various embodiments shown in the appended figures. In the figures, Fig. 1 shows an example of what the capacitor cleaning looks like in one day. follow 2 a first embodiment according to the invention, follow 3 a second embodiment according to the invention and follow 4 a third embodiment according to the invention.

In the usual way for a sulphate pulp use, a stripper 15 is arranged to receive impure condensate 1. The stripper 15 is usually operated with a straight tongs or a reboiler. The steam 4 can be a fresh boot or a steam outlet from the black outlet. The steam 2 out of the stripper 1 is led to a condenser 16 where a part of the condensate 3 is returned to the stripper while non-condensed meadow 6 from the stripper is passed to a methanol colon 17.

The pure condensate 5 from the stripper 15 is returned to the process (b1e- ker1, kem1ka11eàterv1nn1ng) or, for example, an external b1o1og1sk purification is released.

In a normal, more commonly known process, according to FIG.

A second condenser 21 is placed after the first condenser 19 to convert the volatile fraction, methanol, from gas phase 10a to liquid phase 10b. Further, the bottom product 11 from the methanol column 17 passes a decanter 18 where the turpentine is separated while the aqueous phase from the decanter is recycled to the stripper 15. The novelty of the embodiments shown is that an acidifier 7 is added to the methanol column 17 or stripper. To lower the pH. The acidifier can, for example, consist of sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid. formic acid, nitric acid, bisulfite solution, acidic effluents (for example from bleaching plants), residual solution from chlorine dioxide production. carbon dioxide or sulfur dioxide. By adding carbon dioxide or sulfur dioxide, carbon dioxide or sulfuric acid or sulfuric acid are added indirectly, which is formed during the addition of carbon dioxide and sulfur dioxide, respectively.

The acidifier 7 can be added in many different places in the stripper 15 and methanol column 17 of the condensate training or in the feeds to them. This is shown in Figure 2-4 by showing the addition of acidifier 7 in several positions. Normally the addition of acidifier 7 takes place in only one position.

The acidifier 7 is injected, for example, into the liquid base on a distillation bottom located above the inflow 6 to the methanol column 17. The acidifier is added either directly in the liquid on a distillation bottom or in the liquid flow between two distillation bottoms. If highly concentrated acid is used, special mixing equipment may be necessary to add the acid to the liquid in the column. In this case, for example, a liquid stream is pumped out of column 17, whereby the acid is added and the liquid is returned to the column. If carbon dioxide or sulfur dioxide is used as acidifier, this is suitably added directly in the inlet 6 to the methanol column 17. The inlet 6 is usually a gas stream.

Depending on whether there is a problem or not with a high turpentine content in the ammonia-rich stream 11 from the bottom of the methanol column, the methanol column is designed in different ways.

If a high turpentine content can be accepted. the methanol column 17 is formed in the usual way with about 15 distillation bottoms (see figure 2). No decanter is needed as it probably does no good in this case. under normal operating conditions, the turpentine content in stream 11 out of the bottom of the methanol column 17 will be too low to obtain phase separation between water and turpentine. 10 15 20 25 30 35 524 106 If the ammonia-rich stream 11 must be free of turpentine, a modification of the methanol column 17 is required. against a stream of liquid 12 from the methanol column 17. the turpentine 14 separates and returns the remaining fraction 13. In an alternative embodiment (see Fig. 4) a smaller, external column 22 is placed with a small number, for example 5, of destiny bottoms below the decanter 18, which in turn is located below the methanoic ion 17. This additional ion 22 will have the function of driving the turpentine 14 from the ammonia-rich bottom product 11.

The methanol column 17 should be provided with a reboiler 20, since the alternative of using direct steam will mean that the ammonia-rich stream 11 is diluted.

Ammonia will be obtained in the outgoing liquid stream 11 in the form of ammonium salt of the acid used. The continued handling of the ammonia-rich stream 11 depends on where and how it is to be used in the process. Examples of further use are as a nitrogen source in external biological purification, as a fertilizer and for NOx reduction.

If the ammonia is to be used as a nitrogen source (fertilizer) in a biological treatment plant, no further processing of the ammonia-rich stream 11 is required. In this case, however, sulfuric acid should not be used to lower the pH, as sulfuric acid is toxic. If, on the other hand, phosphoric acid is used, this can function as a desired phosphorus addition. This is done by raising the pH, for example by adding white lye, green lye, sodium hydroxide, mesa and other basic currents in the mill. Another alternative is to add the ammonia-rich stream to the melt solvent and thereby drive off the ammonia. The remaining water solution can be reused in the chemical recovery by using the right acidifiers such as sulfur dioxide, sulfuric acid or carbon dioxide. 524 106 To control the rate of acidifier in the methanol column 17, in one embodiment the pH of the methanol column 17 is measured. Examples of measuring points are the outgoing condensate, the bottoms below the t111 flow and above the t111 set of acidifiers. As an alternative to measuring pH, one can control the rate of acidifier depending on the size of some other feed such as the amount of condensate 11 from the coion 17. It is currently preferred to measure the pH above the position where the acidifier 7 is passed. str1ppern 15 e11er metano1ko1onnen 17.

Depending on the intended use, in an alternative embodiment the pH is lowered already in the stripper. This applies above all if the purified condensate is brought to a boiler for a biological treatment. Also in this case the surgeon can be t111 set in the same way as indicated for the methanol column 17.

Claims (1)

1. lO l5 20 25 30 524 106,. . where during the condensate training a volatile fraction comprising methanol is formed, characterized therefrom. that acidifiers are added to the methanol column. Process according to Claim 1, characterized in that the acidifier is fed directly to the methanol column or in the feeds to it. Process according to Claim 2, characterized in that the acidifier consists of either sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, formic acid, nitric acid, bisulfite solution, acidic effluents, residual solution from chlorine dioxide production, sulfur dioxide or carbon dioxide. Process according to Claim 2 or 3, characterized in that additives take place in the liquid on a distillation bottom or in the liquid flow between two bottoms. Process according to any one of the preceding claims, characterized in that a liquid stream is taken out of the methanol column and that the acidifier is added before the liquid stream is returned to the methanol column. 10 5 106 106 Process according to any one of the preceding claims, characterized in that the pH is sensed in the methanol column to regulate the addition of acidifiers. Process according to Claim 6, characterized in that the pH is sensed above the position for the addition of acidifiers. Method according to one of the preceding claims, characterized in that a turpentine decanter is placed a few bottoms up from the bottom outlet in the methanol column. Method according to claim 8, characterized in that the bottoms located below the decanter constitute an external column.