CN107010806B

CN107010806B - Method for treating sludge through hydrothermal carbonization

Info

Publication number: CN107010806B
Application number: CN201710151691.9A
Authority: CN
Inventors: 张镭; 高玉君; 王建宏; 周业剑; 唐军义; 施耐德克劳迪娅; 马克布特曼
Original assignee: Beijing Shunhong Jinjian Environment Technology Development Co ltd
Current assignee: Beijing Shunhong Jinjian Environment Technology Development Co ltd
Priority date: 2017-03-14
Filing date: 2017-03-14
Publication date: 2022-07-12
Anticipated expiration: 2037-03-14
Also published as: CN107010806A

Abstract

The invention provides a method for treating sludge by hydrothermal carbonization, which is characterized in that two acid catalysts are added in two steps, namely, concentrated sulfuric acid is added before entering a reactor, and concentrated nitric acid is added into the reactor in the midway of the reaction.

Description

Method for treating sludge through hydrothermal carbonization

Technical Field

The invention relates to the field of urban domestic sewage treatment, and provides a method for treating sludge through hydrothermal carbonization.

Background

The sludge absorbs a plurality of harmful substances in the sewage and is a concentrated gathering place of the pollutants. The sludge has the characteristics of high water content, easy decay, foul smell, heavy metal content, easy carcinogenesis, teratogenesis, mutagenesis and the like. As an inevitable product in urban operation, the long-term existence of sludge hidden troubles pollutes the environment and seriously threatens the health of people.

The sewage treatment industry in China starts with reformation and has a short history, and is also constrained by the economic development level and the weak environmental protection consciousness. In recent years, although the sewage treatment rate has been improved, the problem of "heavy sewage treatment, but light sludge treatment" has not been solved well: at present, the current situation of treatment and disposal of sludge generated by sewage treatment plants in China is worried. According to statistics of the ministry of environmental protection, sludge agriculture accounts for about 44.8%, land landfill accounts for about 31%, other modes of treatment account for about 10.5%, and no treatment accounts for about 13.7%. These so-called "treatments" and "dispositions" are, in contrast, essentially direct application or landfill, rather than safe dispositions in the true sense, with quantities complying with safety treatment dispositions estimated to be no more than 10%. Various messy phenomena of sludge treatment and disposal are proved in investigation of a plurality of institutions. Sludge which is not treated in a standard way becomes a new environmental pollution source in soil and water environment, the effect of purifying the environment of a sewage treatment plant is counteracted to a great extent, and the healthy development of the sewage treatment industry is seriously restricted.

The difficulty of the treatment of the sludge is determined by the complexity of the composition and the property of the sludge, although various technologies emerge at home and abroad in recent years, the four basic principles of reduction, harmlessness, stabilization and resource are used for measuring, and at present, various different treatment technologies are often considered to be different, so that reasonable technical and economic targets are difficult to achieve: the processes of landfill, fermentation composting and the like which occupy a large amount of land resources and have a absorption period of decades are difficult to become suitable options for sludge treatment; the technical energy consumption of sludge heat drying, incineration and the like is huge, and the technical risk of secondary environmental pollution such as dust, dioxin and the like exists; anaerobic digestion and lime stabilization techniques are only intermediate treatment means, have large floor space and cannot realize the final target of sludge reduction.

The hydrothermal carbonization technology is a novel sludge overall-process treatment and disposal means, and biomass is converted into a carbon-based material, namely biochar, which can be further used as fuels, fertilizers and the like in a wet environment at a certain temperature and pressure. The hydrothermal carbonization technology solves various defects of the traditional treatment process; the method has the advantages of small requirement on the area of the field, suitability for installation equipment of sewage plants, short reaction period, stable operation, high relative efficiency and low energy consumption. But the development time of the hydrothermal carbonization technology is short, and the processing efficiency, the water content of the product, the performance of the biochar, the waste heat utilization and other methods still have a great space for improvement.

Disclosure of Invention

The applicant further optimizes the hydrothermal carbonization treatment process on the basis of introducing German Buttmann hydrothermal carbonization treatment technology to build equipment and actually operating and treating sludge (Beijing, Yanzhou, Jining and the like) of urban domestic sewage plants. In the experiment, the applicant finds that the existing catalyst type and adding mode (concentrated sulfuric acid is added once before entering the reactor) are changed into two times of stepwise adding (concentrated sulfuric acid is added before entering the reactor, and concentrated nitric acid is added into the reactor in the midway of the reaction), so that the water content of the product can be greatly improved, the better sludge reduction effect is realized, the effective nitrogen and phosphorus content is improved, and the chromium content is reduced.

On the one hand, the method for treating the sludge of the municipal domestic sewage plant by hydrothermal carbonization comprises the following steps:

a. collecting sludge;

b. pumping the sludge to a reactor, and adding concentrated sulfuric acid in the reactor;

c. carrying out hydrothermal carbonization reaction in a reactor, and adding concentrated nitric acid during the hydrothermal carbonization reaction;

d. collecting the generated biological carbon slurry.

In a further aspect, the concentrated sulfuric acid used in the process is a 98% concentrated sulfuric acid and the concentrated nitric acid is 80% concentrated nitric acid.

In a further aspect, the concentrated sulfuric acid used in the process is added in an amount of 1-1.5% (v/v) and the concentrated nitric acid is added in an amount of 0.8-1% (v/v).

In a further aspect, the concentrated sulfuric acid used in the process is added in an amount of 1% (v/v) and the concentrated nitric acid is added in an amount of 1% (v/v).

In a further aspect, the hydrothermal carbonization temperature is 150-200 ℃, the pressure is 15-30bar, and the time is 60-150 minutes.

In a further aspect, the hydrothermal carbonization temperature is 180 ℃, the pressure is 25bar, and the time is 120 minutes.

In a further aspect, the hydrothermal carbonization is carried out by adding concentrated nitric acid until one-fourth of the expected reaction time.

And in the step d, the generated biological carbon slurry is collected through a pressure relief system under the condition of ensuring the operation pressure of the system, the heat of the biological carbon slurry is received through a heat exchange system in the period, the obtained heat is used for preheating the sludge in the step b through a front heat exchange system, and the carbon slurry is depressurized through a pressure relief system and then is delivered to a buffer storage tank under residual pressure.

In a further aspect, the pressure in the reactor is provided by a sludge pump.

In a further aspect, the method further comprises a step of plate press dewatering.

Drawings

FIG. 1 is a complete process flow diagram of a sludge hot water carbonization treatment technology. In the figure: 1. feed hopper, 2, mud force (forcing) pump, 3, preceding heat exchanger system, 4, heat recovery, 5, 1# catalyst throw with the point, 6, the reactor, 7, back heat exchanger system, 8, the pressure relief system, 9, the carbon thick liquid storehouse, 10, sheet frame dewatering device, 11, waste water treatment (option), 12, 1# catalyst throw with the pump, 13, 2# catalyst throw with the pump, 14, charcoal heat conduction oil furnace, 15, the filtrating storage tank, 16, the mud feed bin, A, the mud of moisture content 80%, B, deposit repayment (optional), C, the water return mill water inlet after the processing, D, the charcoal cake.

FIG. 2 is an external view of a hydrothermal carbonization apparatus constructed by the applicant and having a treatment capacity of 14000 tons.

Detailed Description

Example 1 sludge treatment in municipal domestic wastewater treatment plant

Sludge sample source: yanzhou city sewage treatment plant, domestic sewage precipitated sludge, the water content is about 80%.

The treatment process of the invention comprises the following steps:

a. collecting sludge by using a closed spiral;

b. pumping the sludge to a reactor, adding 1% (v/v) of 98% concentrated sulfuric acid during the pumping and preheating the sludge by a previous heat exchange system;

c. carrying out hydrothermal carbonization reaction in a reactor, wherein the hydrothermal carbonization temperature is 180 ℃, the pressure is 25bar, the time is 120 minutes, 1% (v/v) of 80% concentrated nitric acid is added when the reaction is carried out for about 30 minutes, and the pressure in the reactor is provided by a sludge pump;

d. collecting the generated biological carbon slurry by a pressure relief system under the condition of ensuring the operating pressure of the system, and cooling and recovering heat by a post heat exchange system in the period;

e. pressing and dehydrating to obtain the charcoal cake.

Control treatment procedure 1:

the basic treatment process is the same as the treatment process of the invention, wherein no acid catalyst is added, and the hydrothermal carbonization temperature is adjusted to 200 ℃, the pressure is adjusted to 30bar, and the time is adjusted to 150 minutes.

Control treatment procedure 2:

the basic process is the same as the process of the present invention, wherein only 2.5% of 98% concentrated sulfuric acid is added as a single catalyst in step b.

Control treatment procedure 3:

the basic treatment process is the same as the treatment process of the invention, wherein only 2.5 percent of 98 percent concentrated sulfuric acid is added as a single catalyst in the step b, and the hydrothermal carbonization temperature is adjusted to 200 ℃, the pressure is adjusted to 30bar, and the time is adjusted to 150 minutes.

The treatment was carried out using the same equipment and the same sludge feed (2.5 tons).

Example 2 comparison of the effects of the treatment methods in example 1

Measuring the water content of the obtained charcoal cake, effective nitrogen content (alkali diffusion method), effective phosphorus content (molybdenum-antimony colorimetric method), and chromium content in the leachate (hexavalent chromium, spectrophotometry)

The result shows that compared with the existing hydrothermal carbonization method, the method can more effectively reduce the water content of the sludge so as to better realize sludge reduction; shortening the reaction time (better than

controls

1 and 3, which have longer reaction times); the effective nitrogen and phosphorus contents in the product are effectively improved to realize better fertilizer effect (even if the difference of water content is eliminated, the effective nitrogen and phosphorus contents of the product of the method are obviously higher than those of the contrast, which is probably caused by a better wall-breaking decomposition process generated by adding two acids step by step); in addition, the products of the process of the invention were also found to have a lower chromium content than the control (the principle is not clear, presumably related to a different carbonisation polymerisation process). The process of the present invention is not significantly different from existing hydrothermal carbonization techniques in terms of construction and operation costs (increased acid species but reduced overall volume).

Claims

1. A method for treating sludge of an urban domestic sewage plant by hydrothermal carbonization comprises the following steps:

a. collecting sludge;

b. pumping the sludge to a reactor, and adding 98% concentrated sulfuric acid in the reactor;

c. carrying out hydrothermal carbonization reaction in a reactor, and adding 80% concentrated nitric acid during the hydrothermal carbonization reaction;

d. collecting the produced biological carbon slurry;

wherein the adding amount of the used concentrated sulfuric acid is 1% v/v, and the adding amount of the concentrated nitric acid is 1% v/v;

wherein the hydrothermal carbonization temperature is 180 ℃, the pressure is 25bar, and the time is 120 minutes;

wherein concentrated nitric acid is added when the hydrothermal carbonization is carried out for one fourth of the expected reaction time;

and d, collecting the generated biological carbon slurry through a pressure relief system under the condition of ensuring the operation pressure of the system in the step d, receiving the heat of the biological carbon slurry through a heat exchange system in the period, preheating the sludge in the step b through a front heat exchange system by the obtained heat, and delivering the residual carbon slurry to a buffer storage tank after the pressure of the carbon slurry is reduced through a pressure relief system.

2. The process of claim 1, wherein the pressure in the reactor is provided by a sludge pump.

3. The process of claim 1, further comprising a step of press dewatering.