From the perspective of the classification of municipal solid waste in cities, they are generally classified according to the composition and quantity of garbage, and the use and treatment of local garbage resources. Such as Germany is generally divided into paper, glass, metal, plastic, etc .; Australia is generally divided into compostable garbage, recyclable garbage, non-recyclable garbage.

(1) Recyclable garbage mainly includes five categories: waste paper, plastic, glass, metal and cloth.

1. Waste paper: mainly including newspapers, periodicals, books, various packaging papers, office papers, advertising papers, paper boxes, etc., but note that paper towels and toilet paper are not recyclable because they are too water-soluble;

2. Plastic: mainly includes various plastic bags, plastic packaging, disposable plastic meal boxes and tableware, toothbrushes, cups, mineral water bottles, toothpaste skin, etc .;

3. Glass: mainly includes various glass bottles, broken glass pieces, mirrors, light bulbs, thermos bottles, etc.

4. Metal objects: mainly including cans, cans, etc .;

5. Cloth: It mainly includes abandoned clothes, tablecloths, face towels, school bags, shoes, etc.

(2) Kitchen waste

Including food waste such as leftovers, bones, root vegetables, peels, etc .;

(3) Harmful garbage

Including waste batteries, waste fluorescent tubes, wastewater silver thermometers, expired medicines, etc., these wastes need special safety treatment;

(4) Other garbage

Including bricks and ceramics, muck, toilet paper, paper towels and other wastes that are difficult to recycle except the above types of garbage.

With the rapid development of industries such as construction, road construction, and water conservancy engineering, more and more users are investing in cement production lines, but some users do not know much about the cement production process. This article makes a simple analysis of the cement rotary kiln process, which is convenient. Users understand.

1. Cement production process

The cement production process uses a new dry cement preparation process, which is mainly composed of crushing and pre-homogenization, raw material preparation and homogenization, pre-heat decomposition, cement clinker firing, cement grinding and packaging, etc. And grind, or dry and grind into raw meal powder, then feed the raw meal powder into the cement rotary kiln to calcinate the mature material, and then add the appropriate amount of gypsum (sometimes with mixed materials or additives) MBS type rod mill is finely ground.

Crushing and pre-homogenization

(1) Crush During the cement production process, most of the raw materials are crushed, such as limestone, clay, iron ore and coal. Limestone is the raw material that produces the largest amount of cement. After mining, the particle size is larger and the hardness is higher. Therefore, the crushing of limestone plays an important role in the crushing of the cement plant.

(2) Pre-homogenization of raw materials Pre-homogenization technology is the use of scientific stacking and reclaiming technology during the storage and retrieval of raw materials to achieve the initial homogenization of raw materials, so that the raw material yard has both storage and homogenization functions.

Raw material preparation

During the cement production process, at least 3 tons of materials (including various raw materials, fuels, clinkers, mixtures, and gypsum) must be ground for each ton of portland cement. According to statistics, the grinding operation of dry cement production lines requires consumption The power of the plant accounts for more than 60% of the plant’s power, of which raw material grinding accounts for more than 30%, coal grinding accounts for approximately 3%, and cement grinding accounts for approximately 40%. Therefore, reasonable selection of grinding equipment and process flow, optimization of process parameters, correct operation, and control of the operating system are of great significance for ensuring product quality and reducing energy consumption.

Raw material homogenization

In the new dry cement production process, the stability of the raw material composition in the cellar is the prerequisite for the stable thermal system of clinker firing. The raw material homogenization system plays the final role of stabilizing the raw material composition in the rotary cellar.

Preheat decomposition

The preheater and partial decomposition of the raw materials are completed by the preheater, which replaces some functions of the rotary kiln to shorten the length of the return kiln. At the same time, the kiln is stacked to perform the gas-material heat exchange process and moved to the preheater in a suspended state The following processes are carried out so that the raw material can be fully mixed with the hot gas discharged from the kiln, which increases the contact area of ​​the gas material, the heat transfer speed is fast, and the heat exchange efficiency is high. purpose.

Firing of cement clinker

In the rotary kiln, the carbonate is further rapidly decomposed and a series of solid phase reactions occur to generate cement clinker. After a series of chemical reactions, the high temperature clinker discharged from the rotary kiln is cooled by the cement clinker cooler. To a reasonable temperature, while recovering the waste heat of the high-temperature clinker, improving the thermal efficiency and clinker quality of the rotary kiln.

Cement grinding

Cement grinding is the last process of cement manufacturing, and it is also a process that consumes a lot of power. Its main function is to grind cement clinker (and gelling agent, performance adjusting materials, etc.) to a suitable particle size (represented by fineness, specific surface area, etc.) to form a fine particle size that meets the requirements and increase its water content. It can accelerate the hydration rate and meet the requirements of cement slurry setting and hardening.

In general, the process of cement rotary kiln is crushed, batched, and ground to make raw materials, then homogenized, and then slowly calcined mature materials in the cement rotary kiln. After the finished product, it can be sent to the material end.

At present, the treatment methods of medical waste mainly include sanitary landfill method, high temperature incineration method, pressure steam sterilization method, chemical sterilization method, electromagnetic wave sterilization method, plasma method, dry heat sterilization method, pyrolysis method, and the like.

Sanitary landfill method

Sanitary landfill method is the final disposal method of medical waste. Its principle is to bury garbage in the ground and decompose it into harmless substances through long-term decomposition of microorganisms. If the landfill system of medical waste does not have anti-seepage measures, various toxic substances, pathogens, and radioactive substances will seep into the soil with rainwater, and harmful substances will enter the human body through the food chain, endangering human health. Therefore, the sanitary landfill needs to be scientifically selected and laid with an anti-seepage layer using clay, high-density polyethylene, and other materials. Landfill gas collection and output pipelines must be set up. Therefore, the landfill treatment method must be used very carefully. Strict pretreatment of medical waste in accordance with relevant regulations.

High-temperature incineration

Medical waste is mainly composed of organic hydrocarbons, contains more flammable components, has a high calorific value, and it is completely feasible to use incineration. Incineration is a chemical process that is deeply oxidized. Under the action of a high-temperature flame, the medical waste in the incineration equipment is dried, ignited, and incinerated to convert it into residues and gases. The source of infection in medical waste And harmful substances can be effectively destroyed during the incineration process. The incineration technology is suitable for various infectious medical wastes. During incineration, a high and stable furnace temperature, good oxygen mixing conditions, sufficient gas retention time, and other conditions are required. Gas and residues are detoxified.

Chemical disinfection method

The essence of the chemical disinfection method is to mix the crushed medical waste with a certain concentration of disinfectant (sodium hypochlorite, peroxyacetic acid, glutaraldehyde, ozone, etc.) and ensure that it has sufficient contact area and time with the disinfectant. Organic matter is decomposed and microorganisms are killed during the disinfection process. The maximum contact between disinfectant and medical waste is a prerequisite to ensure the treatment effect. The use of rotary crushing equipment improves the degree of crushing and ensures that the disinfectant can penetrate it. Chemical disinfection is suitable for the treatment of liquid medical waste and pathological waste. Recently, it is also gradually used for the treatment of medical waste that cannot be sterilized by heating or wetting.

High-temperature pyrolysis incineration

The principle of high-temperature pyrolysis method is to heat the organic components of medical waste to 6OO ～ 900 ~ C under oxygen-free or oxygen-depleted conditions, use thermal energy to break the compound bonds, and convert large molecular weight organic matter into flammable gas. Process of liquid fuel and coke. The gas produced by pyrolysis mainly contains hydrogen, methane, carbon monoxide, carbon dioxide, and other hydrocarbons and volatile organic compounds.

With the acceleration of China’s urbanization process and the rapid development of society and economy, the intensity of sewage treatment has gradually increased, and the sludge generated therefrom has increased dramatically. At the same time, due to the improvement of China’s environmental standards, sludge is in urgent need of advanced treatment.

Common sludge treatment technologies

The sludge treatment technologies mainly include sludge digestion, drying, composting and incineration.

(1) Sludge digestion

Sludge digestion includes aerobic digestion and anaerobic digestion. The purpose of aerobic digestion is to stabilize the sludge, reduce the harm of the sludge to the environment and soil, and reduce the final treatment capacity of the sludge. The sludge digestion method has the advantages of stability and sterilization, low investment, convenient operation and management, low capital construction costs, odorless final product, and low concentration of supernatant at night, so it is particularly suitable for sludge treatment in small and medium-sized sewage plants. The purpose of anaerobic digestion is to reduce sludge volume and stabilize sludge properties.

(2) Drying

The most effective way to reduce weight is to dry. Drying means that a certain amount of heat energy is transferred to the moisture contained in the material in a unit time. These moisture are vaporized after being heated, separated from the material, and the material that has lost the moisture is vaporized. The moisture content is collected separately, which is the drying process. Sludge drying can reduce the water content from 70% to less than 10%. In fact, according to the needs of final disposal, the final solids content of sludge can vary between 60% and 95%. At this time, the reduction of sludge exceeds 60%, which is more reasonable in terms of cost and safety.

Drying is divided into direct and indirect heating methods, mainly due to the difference in the form of heat source utilization, specifically, directly as a medium or indirectly heating the heat-exchanging medium. Drying is accomplished by heat, which is generally generated by energy combustion.

(3) Sludge compost

Sludge composting is a process of aerobic fermentation using aerobic microorganisms in sludge. It is a self-generating process that can eliminate pathogens and produce a substance similar to humus. Generally, it can be divided into separate compost , Sludge and garbage mixed compost.

(4) Sludge incineration

Sludge incineration can destroy all organic matter, kill all pathogens, and minimize the volume of sludge. The sludge with a relative water content of incineration residue of about 75% is only about 10% of the original volume. When the combustion heat value of the sludge itself is high, the urban sanitary requirements are high, the land is tight, or the sludge has a high content of toxic substances and cannot be comprehensively used, it can be treated by incineration. Before the sludge is incinerated, it should generally be dehydrated and thermally dried to reduce the load and energy consumption. Sludge incineration is technically feasible and has reached an industrial scale.

The characteristics of incineration treatment: greatly reduce the volume and weight of sludge; kill all pathogens; the sludge treatment speed is fast and does not require long-term storage; energy can be recovered. But on the other hand, its higher operating costs and flue gas treatment issues have become the main factors restricting the sludge incineration process.

Common sludge disposal technology

The sludge disposal technologies mainly include resource utilization such as landfill, land use and building materials.

(1) Sanitary landfill of sludge

The sanitary landfill of sludge began in the 1960s. It is based on traditional landfills after scientific site selection and necessary site protection treatment. It has a strict management system and scientific engineering operation methods. Landfill is a relatively mature disposal technology, which has the advantages of simple disposal method, large processing capacity, quick results, easy operation, low cost, no need for high dehydration, and strong adaptability. However, the large land area occupied by sludge landfills has caused most landfill sites to be reluctant to accept sludge under the current shortage of urban land. In addition, there are problems with the management system and management departments cannot clearly distinguish responsibilities. Therefore, the prospect of sludge sanitary landfill is not optimistic.

(2) Use of sludge land

At present, the land use types of sludge are many and extensive, such as agricultural and forestry arable land, animal husbandry grassland, garden green land and so on. Land use of sludge refers to the use of soil’s self-purification ability to harmlessly treat sludge. The effective components of sludge can improve soil structure and promote plant growth. It is a better soil improver. This method of disposal is the application of sludge to farmland, municipal greening, nursery substrates and land restoration and reconstruction and replacement of landfill clay. However, considering the heavy metals and harmful substances contained in the sludge itself, and the inadequate acceptance of sludge products by farmers and consumers, and incomplete national relevant policies and norms and standards, domestic sludge farming has struggled.

(3) Comprehensive utilization of building materials

The use of sludge to produce building materials can realize the full use of resources and energy, and can also decompose or solidify the toxic and harmful substances therein. The resource utilization of sludge manufacturing construction materials has significant advantages, and it will be one of the important development directions of sludge resource technology. The building material industry has a very large demand for raw materials, which can absorb a large amount of sludge on site, and has broad application prospects. The currently known methods for building sludge from sludge include bricks from sludge, cement from sludge production, and lightweight ceramsite materials from sludge.

Status and development trend of sludge treatment and disposal

Most of the sludge from urban sewage treatment plants is disposed of in landfills. Some of them are professional landfills, and some are mixed with municipal waste. A small part is disposed of for agricultural use, including returning to the field after stabilization and returning to the field after composting. There is also a part for incineration. The sludge volume of point source facilities in enterprises is relatively small, and the cost of disposal is relatively high. Basically, the enterprise disposes it by itself. According to the nature of sludge, there are various disposal methods.

Development trend

With the continuous progress of environmental protection science and technology, China’s sludge treatment and disposal technology will gradually catch up with the international development trend of sludge disposal, from landfill to incineration disposal, land use, building material use and other comprehensive utilization methods. .

With the increase of urban sewage discharge and treatment rate in China, sludge production has increased significantly, and sludge treatment and disposal are facing new challenges. Therefore, it is urgent to seek solutions based on China’s national conditions and sludge characteristics. The sludge should be turned into a usable substance under the principle of “reduction, stabilization, harmlessness, and recycling” to realize resource recycling and promote the development of circular economy. With the country’s increasing emphasis on environmental protection and increased investment, the technology for sludge treatment and disposal will surely be further developed and improved.

Divided into five categories according to the waiting, hazardous, material and disposal methods of medical waste: Infectious waste; Damaging waste; Pathological waste; Pharmaceutical waste; Chemical waste.

Infectious waste

Characteristics: Medical wastes that carry pathogenic microorganisms are at risk of spreading infectious diseases. mainly include:

1. Items contaminated by patient’s blood, body fluids, and feces, including:

① Cotton balls, cotton swabs, drainage slivers, gauze and various other dressings;

② Disposable sanitary products, disposable medical supplies and disposable medical devices;

③ Abandoned quilts;

④ Other items contaminated by the patient’s blood, body fluids, and feces.

2. Isolation of domestic waste from infectious disease patients or suspected infectious disease patients admitted by medical institutions;

3. Pathogen’s culture medium, specimens, strains, and virus preservation solution;

4. Various abandoned medical specimens;

5. Discarded blood and serum;

6. Disposable medical supplies and disposable medical devices after use are regarded as infectious waste.

Damaged waste

Features: Discarded medical sharps that can stab or cut the human body. Mainly include:

1. Medical needles and suture needles;

2. Various types of medical sharps, including: scalpels, scalpels, skin preparation knives, surgical saws, etc .;

3. Glass slides, glass test tubes, glass ampoules, etc.

Pathological waste

Features: human waste and medical laboratory animal carcasses generated during diagnosis and treatment. Mainly include:

1. Discarded human tissues and organs generated during surgery and other diagnosis and treatment;

2. Tissues and corpses of medical experimental animals;

3. Discarded human tissue and pathological wax blocks after pathological sectioning;

4. Placenta of infectious diseases, suspected infectious diseases and infectious diseases of unexpected causes;

Pharmaceutical waste

Features: Obsolete medicines that are out of date, obsolete, deteriorated or contaminated. Mainly include:

1. Discarded generic drugs, such as antibiotics and over-the-counter drugs;

2. Discarded cytotoxic drugs and genotoxic drugs, including:

① Carcinogenic drugs, such as thiopurine, phenylbutyric acid mustard, naphthalene mustard, cyclosporine, cyclophosphamide, phenylalanine mustard, smelastine, tamoxifen, thiotepa, etc .;

② Suspected carcinogenic drugs, such as: cisplatin, mitomycin, doxorubicin, phenobarbital, etc .;

③ immunosuppressive agents.

3. Discarded vaccines, blood products, etc.

Chemical waste

Features: Waste chemicals that are toxic, corrosive, and flammable and explosive. Mainly include:

1. Discarded chemical reagents in medical imaging rooms and laboratories;

2. Discarded chemical disinfectants such as peroxyacetic acid and glutaraldehyde;

3. Discarded mercury sphygmomanometers and mercury thermometers.