CN108178470B

CN108178470B - Method for one-step recovery of phosphorus from algae mud by supercritical water gasification

Info

Publication number: CN108178470B
Application number: CN201810023204.5A
Authority: CN
Inventors: 朱伟; 陈程; 王辰宇; 张颢; 林乃喜; 范惜辉; 崔岩
Original assignee: Hohai University HHU
Current assignee: Hohai University HHU
Priority date: 2018-01-10
Filing date: 2018-01-10
Publication date: 2020-04-21
Anticipated expiration: 2038-01-10
Also published as: CN108178470A

Abstract

The invention discloses a method for recovering phosphorus from algae mud by one step by supercritical water gasification, which utilizes water which is difficult to remove in the algae mud as a reaction medium under a supercritical condition to decompose organic matters in the algae mud, and adds an alkaline additive to ensure that phosphorus mainly exists in a liquid form after the algae mud is subjected to supercritical water gasification reaction, so that a liquid-phase product containing a large amount of ammonia nitrogen and phosphorus is directly utilized as a recovery matrix, a magnesium source is added to carry out one-step recovery on the phosphorus in the liquid-phase product by an MAP method, and the obtained struvite crystal can be used as an agricultural fertilizer. The invention solves the problem that most of phosphorus enters a solid-phase product and needs to be leached for the second time when the phosphorus is recovered from algae mud by supercritical water gasification, and the phosphorus basically enters a liquid-phase product by adding a specific basic additive, thereby realizing one-step recovery of the phosphorus by an MAP method, greatly simplifying the steps of phosphorus recovery, saving the cost and improving the recovery efficiency.

Description

Method for one-step recovery of phosphorus from algae mud by supercritical water gasification

Technical Field

The invention belongs to the field of resource environment, and particularly relates to a method for recovering phosphorus from algae mud by one step through supercritical water gasification.

Background

The cyanobacterial bloom in China frequently bursts and has serious harm to the environment. At present, fishing is a common measure adopted by China for pollution caused by cyanobacterial bloom, and according to statistics, the accumulated fishing algae liquid from Taihu lake in Jiangsu province in 2015 reaches 164 ten thousand tons, which increases the fishing amount by 44 thousand tons compared with 2014. The fished algae liquid enters an algae-water separation station to be dewatered and flocculated to form sludge which is called algae sludge, so that a great amount of algae liquid generates a great amount of algae sludge which is difficult to treat. How to reduce and harmlessly treat the algae mud and realize resource utilization is the key for treating the cyanobacterial bloom and safely treating and disposing the algae mud.

At present, the common algae mud treatment and disposal modes at home and abroad comprise landfill, incineration, anaerobic fermentation from the resource utilization perspective, land utilization after composting, pyrolysis and the like, but due to the characteristics of high water content and cell structure as the main characteristics of the algae mud, the energy consumption and the efficiency of pretreatment processes such as dehydration and drying are high, so that the harmless treatment and the resource utilization of the algae mud are severely restricted. The supercritical water gasification treatment technology directly utilizes the water which is difficult to remove in the algae mud to decompose the organic matters in the algae mud in a supercritical state, thereby achieving the purposes of reduction and harmless treatment and recycling the generated hydrogen and N, P in the product to realize resource utilization.

The Chinese patent with the application number of 201410787213.3 provides a device and a method for recovering nitrogen and phosphorus by supercritical water gasification products of blue algae liquid, but the patent uses a two-step method to recover P, and the P in a solid phase is extracted by adding acid liquor in an oscillating way and enters a liquid phase, and then the P is recovered from a leaching solution.

Disclosure of Invention

The invention aims to provide a method for recovering phosphorus from algae mud in one step by supercritical water gasification, which is characterized in that basic additives are added to ensure that phosphorus mainly exists in a liquid phase after reaction, so that a liquid-phase product meets the grade and concentration of phosphorus recovery, nitrogen and phosphorus can be directly recovered from the liquid-phase product in one step, the process steps are simplified, the process time and the cost are saved, and the aim of resource utilization of the algae mud is fulfilled.

The invention is realized by the following technical scheme:

a method for recovering phosphorus from algae mud in one step by using supercritical water gasification comprises the following steps:

step 1) mixing the algae mud and the basic additive evenly, and injecting the mixture into a supercritical water gasification reactor through a high-pressure pump for reaction;

after the reaction in the step 2), carrying out gas-liquid-solid three-phase separation on the reaction product, wherein the gas-phase product is hydrogen-rich gas and can be directly recycled; treating the liquid phase product by a struvite precipitation method, discharging and collecting the generated supernatant, performing subsequent treatment, and recovering the generated struvite crystals to be used as agricultural fertilizer.

Further, in the step 1), the reaction pressure is set to be 22-25 MPa, the reaction temperature is set to be 400-500 ℃, and the reaction residence time is 10-30 min.

Further, the basic additive in the step 1) is KOH and K₂CO₃、NaOH、Na₂CO₃One or a mixture of more than one of them.

Further, the addition amount of the basic additive in the step 1) is 2-8% of the mass of the algae mud.

Further, the basic additive in the step 1) is in a powder form.

Further, the reaction pH value of the struvite precipitation method in the step 2) is maintained at 8.5-10.5.

The invention has the following beneficial effects:

the method of the invention promotes the phosphorus to be concentrated in the liquid phase product by doping the basic additive into the algae mud, thereby directly taking the liquid phase product as a recycling matrix and recycling the nitrogen and phosphorus as agricultural fertilizer by a MAP method and struvite crystallization. The invention improves the conventional two-step phosphorus recovery into one-step phosphorus recovery, omits the process step that the phosphorus can be further recovered after the solid-phase product is leached by acid liquor to release the phosphorus into the liquid phase in the conventional phosphorus recovery method, and greatly saves the process time and the cost.

Drawings

FIG. 1 is a flow chart of a method of the present invention;

FIG. 2 is a schematic view of the apparatus of example 1.

In fig. 2: 1. an algae mud storage tank; 2. a basic additive storage tank; 3. a basic additive control valve; 4. a basic additive quantitative feeder; 5. a feed regulating valve; 6. a algae mud control valve; 7. an algae mud pretreatment tank; 8. an inlet valve; 9. a high pressure plunger pump; 10. an outlet valve; 11. a first heat exchanger; 12. a back pressure valve; 13. a supercritical water gasification reactor; 14. a system pressure regulating valve; 15. a second heat exchanger; 16. a gas-liquid flow valve; 17. a gas-liquid-solid separation tank; 18. a gas-liquid separation tank; 19. a wet gas flow meter; 20. a drying chamber; 21. a liquid flow meter; 22. a MAP reaction tank; 23. a pH on-line monitor; 24. a pH adjusting tank; 25. a stirring motor; 26. a magnesium chloride storage tank; 27. a magnesium chloride control valve; 28. magnesium chloride quantitative feeder.

Detailed Description

The invention is further explained below with reference to the drawings and the examples.

A method for recovering phosphorus from algae mud by supercritical water gasification in one step is shown in figure 1, and comprises the following steps:

step 1: uniformly mixing the algae mud and the basic additive, and injecting the mixture into a supercritical water gasification reactor through a high-pressure pump, wherein the reaction pressure is set to be 22-25 MPa, the reaction temperature is set to be 400-500 ℃, and the reaction residence time is 10-30 min;

step 2: after the reaction is finished, gas-liquid-solid three-phase products are separated, phosphorus is directly recovered from liquid-phase products of supercritical water gasification by a struvite (MAP) precipitation method, and high-quality struvite is generated.

As a further improvement of the invention, in the step 1, the basic additive is added into the algae mud before the supercritical water gasification reaction, the purity requirement of the additive reaches analytical purity, and the phosphorus in the algae mud is generated in a liquid form after the supercritical water gasification reaction and can reach the grade with the phosphorus concentration of more than 70 percent, thereby realizing the aim of recovering the phosphorus in one step.

As a further improvement of the invention, in the step 1, the basic additive comprises KOH and K₂CO₃、NaOH、Na₂CO₃The basic additive can be added singly or in a mixed manner, and the addition amount of the basic additive is 2 to 8 percent of the mass of the algae mud, and the basic additive is added in a powder form.

Example 1

The method of the present invention will be described in more detail with reference to specific apparatuses, which are shown in fig. 2 and include an algae mud storage tank 1, an alkali additive storage tank 2, an alkali additive control valve 3, an alkali additive quantitative feeder 4, a feed regulating valve 5, an algae mud control valve 6, an algae mud pretreatment tank 7, an inlet valve 8, a high-pressure plunger pump 9, an outlet valve 10, a first heat exchanger 11, a back pressure valve 12, a supercritical water gasification reactor 13, a system pressure regulating valve 14, a second heat exchanger 15, a gas-liquid flow valve 16, a gas-liquid-solid separation tank 17, a gas-liquid separation tank 18, a wet gas flow meter 19, a drying chamber 20, a liquid flow meter 21, a MAP reaction tank 22, an online pH monitor 23, a pH regulating tank 24, a stirring motor 25, a magnesium chloride storage tank 26, a magnesium chloride control valve 27, and a magnesium chloride quantitative feeder 28.

Wherein, the output pipe of the algae mud storage tank 1 is connected to the first input pipe of the algae mud pretreatment tank 7 through the algae mud control valve 6, the output pipe of the basic additive storage tank 2 is connected with the second input pipe of the algae mud pretreatment tank 7 through the basic additive control valve 3, the basic additive quantitative feeder 4 and the feed regulating valve 5 in sequence, the output pipe of the algae mud pretreatment tank 7 is connected with the input pipe of the first heat exchanger 11 through the inlet valve 8, the high-pressure plunger pump 9 and the outlet valve 10 in sequence, the output pipe of the first heat exchanger 11 is connected with the input pipe of the supercritical water gasification reactor 13 through the back pressure valve 12, the output pipe of the supercritical water gasification reactor 13 is connected with the input pipe of the second heat exchanger 15 through the system pressure regulating valve 14, the output pipe of the second heat exchanger 15 is connected with the input pipe of the gas-liquid-solid separation tank 17 through the gas-liquid flow valve 16, the first output pipe of the gas-liquid-solid separation tank 17 is, a second output pipe of the gas-liquid-solid separation tank 17 outputs a solid-phase product;

a first output pipe of the gas-liquid separation tank 18 is connected with an input pipe of a drying chamber 20 through a wet gas flowmeter 19, an output pipe of the drying chamber 20 outputs hydrogen-rich gas, a second output pipe of the gas-liquid separation tank 18 is connected with a first input pipe of an MAP reaction tank 22 through a liquid flowmeter 21, an input pipe of a magnesium chloride storage tank 26 is connected with a second input pipe of the MAP reaction tank 22 through a magnesium chloride control valve 27 and a magnesium chloride quantitative feeder 28 in sequence, the first output pipe of the MAP reaction tank 22 outputs supernatant, the second output pipe outputs struvite crystals, a pH on-line monitor 23 is connected with a pH adjusting tank 24 in parallel and then inserted into the MAP reaction tank 22 through a pipeline, and a fan blade of a stirring motor 25 is arranged in the MAP reaction tank 22.

The method for recovering phosphorus from the algae mud by using the device comprises the following steps:

1. mixing the algae mud and an alkaline additive KOH in an algae mud pretreatment tank 7 (taking the KOH mixing amount as an example of 6%), adjusting the pressure to 22-25 MPa by a high-pressure plunger pump 9, heating to 400-500 ℃ by a first heat exchanger 11, and reacting for 10-30 min in a supercritical water gasification reactor 13.

2. After the supercritical water gasification reaction is finished, opening a system pressure regulating valve 14 to reduce pressure, enabling a gas-liquid-solid mixed phase product to enter a second heat exchanger 15 for cooling treatment, opening a gas-liquid flow valve 16 to enter a gas-liquid-solid separation tank 17, obtaining a solid phase product through the gas-liquid-solid separation tank 17, performing gas-liquid separation through a gas-liquid separation tank 18, discharging the gas phase product through a first output pipe at the top of the gas-liquid separation tank 18, and drying the gas phase product through a wet gas flowmeter 19 to obtain a hydrogen-rich gas after the gas phase product enters a drying chamber 20.

3. The liquid phase product enters an MAP reaction tank 22 through a liquid flowmeter 21, the acid-base environment in the MAP reaction tank 22 is adjusted through a pH on-line monitor 23 and a pH adjusting pool 24, the pH is maintained between 8.5 and 10.5, magnesium chloride is conveyed into the MAP reaction tank 22 through a magnesium chloride quantitative feeder 28, and is stirred and dissolved by a stirring motor 25 to participate in MAP reaction.

4. After the MAP reaction is finished, the supernatant is discharged and collected by a first output pipe of the MAP reaction tank 22 and is subjected to subsequent treatment, and the generated struvite crystals are discharged and collected by a second output pipe at the bottom of the MAP reaction tank 22 and are used as agricultural fertilizer. The reaction results are shown in table 1.

Example 2

The difference from example 1 is that the kind of basic additive is replaced with K₂CO₃The reaction results are shown in Table 1.

Example 3

The difference from example 1 was that the kind of basic additive was replaced with NaOH, and the reaction results were as shown in Table 1.

Example 4

The difference from example 1 is that the kind of basic additive was replaced with Na₂CO₃The reaction results are shown in Table 1.

TABLE 1

When the algae mud is directly subjected to supercritical water gasification reaction (without additives), the liquid phase TP grade is only 11.57%, and the concentration is only 35.13 mg/L. As can be seen from Table 1, after the basic additive is doped, the grade and concentration of phosphorus in the liquid phase are greatly improved, wherein the KOH effect is optimal, and the grade and concentration of the phosphorus in the liquid phase meet the recovery requirement of an MAP method, so that the recovery of phosphorus from a solid-phase product by a two-step method is improved into the recovery of phosphorus from a liquid-phase product by a one-step method.

Claims

1. A method for recovering phosphorus from algae mud in one step by utilizing supercritical water gasification is characterized by comprising the following steps:

step 1) mixing the algae mud and the basic additive evenly, and injecting the mixture into a supercritical water gasification reactor through a high-pressure pump for reaction; the basic additive is KOH and K₂CO₃、NaOH、Na₂CO₃One or a mixture of more than one of them;

2. The method for one-step recovery of phosphorus from algae mud by supercritical water gasification according to claim 1, wherein the reaction pressure in step 1) is set to 22-25 MPa, the reaction temperature is set to 400-500 ℃, and the reaction residence time is 10-30 min.

3. The method for one-step recovery of phosphorus from algae mud by supercritical water gasification according to claim 1, wherein the addition amount of the basic additive in step 1) is 2-8% of the mass of algae mud.

4. The method for one-step recovery of phosphorus from algae mud by supercritical water gasification according to claim 1, wherein the basic additive in step 1) is in powder form.

5. The method of claim 1, wherein the struvite precipitation process of step 2) is performed at a reaction pH of 8.5-10.5.