Українська   Русский
DonNTU Masters' portal

Abstract

Содержание

Introduction

Electricity is a key global industry that determines the technological development of humanity in the global sense of the word. This industry includes not only the whole range and variety of methods of production (generation) of electricity, but also its transportation to the end consumer in the face of industry and society as a whole. The development of the electric power industry, its perfection and optimization, designed to meet the constantly growing demand for electricity, is a key global global task of today and the foreseeable future.

Thermal power plant (TPP) is a major source of pollution of the atmosphere, hydrosphere, lithosphere. The main sources of lithosphere pollution are ash dumps and sludge ponds.

At TPPs, during the production of electrical and thermal energy, as a result of the preparation of large volumes of water to replenish the losses associated with the release of process steam for production, significant volumes of water treatment waste - chemical water treatment sludge (CWT) are generated.

CWT sludge is a product of liming and coagulation of natural water.

At present, the sludge of the CWT TPP is disposed of as hazard class V waste. These sludges are formed at the stage of preliminary water purification, which includes water clarification (liming and coagulation processes), as well as reducing alkalinity and softening it.

Sludge waste is accumulated in surface storages, which are not equipped with means of protecting the environment from seepage waters. The sludge does not contain highly toxic substances, but problems with the storage of this waste remain. At the same time, large areas are alienated, there is a threat of salinization, mineralization of groundwater in adjacent territories and a violation of the hydrochemical regime of nearby water bodies. In many developed countries, they refuse to store sludge in sludge ponds that pose a threat to the environment. Currently, there is no universal method for the treatment and disposal of chemical water treatment sludge.

1. Theme urgency

In the process of generating heat and electricity at the Starobeshevskaya TPP, a large-tonnage sludge of chemical water treatment is formed.

Sludge collectors used for long-term accumulation of sludge from water treatment shops are a source of environmental pollution, the negative impact of which is expressed by filtration of suspensions into the soil and groundwater, as well as the secondary removal of dust from the surface of the slime collector.

Therefore, despite the age and a large number of studies in the field of environmentally friendly production, the problem of utilization and processing of industrial waste remains relevant to this day. Therefore, there is an economically, technologically and environmentally justified need to develop and implement more and more progressive and safe methods for solving waste disposal in the form of sludge from the chemical water treatment plant at Starobeshevskaya TPP.

2. Object, goals, objectives of the study

The purpose of the work is to develop a technology for disposal of sludge from the chemical water treatment plant.

To achieve this goal, the following tasks were identified:

  1. Describe the process of sludge formation in the chemical water treatment plant.
  2. Review existing sludge disposal methods.
  3. Taking into account the chemical and phase composition of the sludge from the chemical water treatment plant at Starobeshevskaya TPP, develop a sludge disposal technology.
  4. To make an ecological and economic assessment of the developed measures.

Object of study: sludge from the chemical water treatment plant at Starobeshevskaya TPP.

Scientific novelty:: as a result of research, an environmentally friendly technology for the disposal of sludge from the chemical water treatment plant at Starobeshevskaya TPP is being developed.

Starobeshevskaya TPP

Figure 1 – Starobeshevskaya TPP

3. Sludge formation process

Sludge wastes from water treatment of thermal power plants are formed at the stage of water clarification of the technological process of purification, desalting and softening of water, which is supplied to steam turbine units of thermal power plants. Sediment in the form of slurry pulp is formed in clarifiers when coarse and colloidal impurities are removed from water by simultaneous liming and coagulation using Ca(OH)2 lime and FeSO4 coagulant.

Studies of the chemical composition of water treatment sludge from Starobeshevskaya TPP showed that the main ingredients are compounds of Ca, Si, Mg, Fe, alumina and an insignificant content of sulfur–containing compounds. This confirms that the insoluble sludge substances are composed of calcium and magnesium compounds and partly of alumina-ferrous substances. Approximately 30 % in sludge is organic matter [1].

The composition of the slimes formed during liming and coagulation of natural waters depends on the composition of the treated water and treatment modes, but in all cases the main components are calcium carbonate (75–85%), as well as magnesium and iron hydroxides (4–8% of each component) and silicic acid and organic compounds.

The use of carbonate sludge is possible only after dehydration or drying at a constant temperature of 120–130 C. Dried sludge is a loose powder from gray to brown color with a moisture content of no more than 20% and a mass fraction of calcium and magnesium carbonates – 80–88%.

At TPPs of average power, about 20 tons of sludge is formed daily, that is, per year, in terms of dry matter, this is about 7300 tons.When TPPs operate on solid fuel, CWT sludge is mostly lost, since they are sent to the hydraulic ash removal system, mixing with the ash part solid fuel. TPPs that burn gas or fuel oil have sludge accumulators, into which the chemical water treatment sludge is supplied in the form of pulp, in an amount of up to 900 m3 / day. or about 330 thousand m3 per year. Sludge collectors occupy from 1000 to 3000 hectares [2].

Large volumes of accumulated sludge represent a serious problem as Cleaning of sludge dumps and disposal of large–capacity waste water treatment are associated with a number of economic and environmental problems. At present, the sludge of the chemical water treatment plant is stored in the sludge dumps.

After filling the sludge dumps to the design level, the discharge of sludge water is stopped, the sludge dump is left to dehydrate the sludge with the aim of its subsequent cleaning and preparation for further temporary accumulation of waste. In this regard, the biggest problem in the energy sector is the formation and disposal of a large amount of CWT sludge, which accumulates over several years on sludge dumps, contributing to the alienation of large areas for its storage.

The development of methods for the disposal of industrial waste to obtain economically useful products allows to reduce the consumption of natural resources and create a real basis for rational (balanced) environmental management [3].

4. Review of existing sludge disposal methods

Considering the significant amount of accumulated sludge, safety, availability and low cost, they have good prospects for widespread use. After analyzing the literature data, we have selected the most promising methods for the disposal of CWT sludge:

  1. Use of CWT sludge in the construction industry.
  2. The use of sludge of clarifiers for chemical water treatment of TPPs in the production of polymer composites.
  3. Use of CWT sludge as a mineral fertilizer.
  4. Use of CWT sludge as adsorbent.

Since the resulting sludge contains a large amount of calcium carbonate, it is mainly used in the construction industry, for the production of cement, building lime, for the production of gypsum binder. It has been established that the production of gypsum based on CWO sludge should be carried out under autoclave conditions: temperature – 139 C, pressure – 0,25 MPa, processing time – 2,0–2,5 hours. According to the proposed technology, the CWT sludge after neutralization with sulfuric acid is autoclaved according to the above regimes, after which it is mechanically dewatered and dried in a dryer. [4].

At present, there is a rapid growth in the use of sludge from CWT TPPs as a mineral inert filler in rubber compounds, which makes it possible to reduce the cost of its disposal, and to entrepreneurs–manufacturers – to reduce the cost of production by using cheaper raw materials.

The chemical composition of the waste water treatment plant sludge makes it possible to use it as a mineral fertilizer – to neutralize acidic soils, since the water environment of the chemical water treatment plant sludge is alkaline.

One of the ways to utilize the sludge of chemical water treatment is to use it as a sorbent for the purification of wastewater from thermal power plants from oil products. Based on carbonate sludge, a special granular hydrophobic sorbent is used [5].

5. Selection and substantiation of the most effective method for disposal of sludge from the chemical water treatment plant at Starobeshevskaya TPP

From the point of view of environmental safety, the most acceptable technologies for implementation at production facilities are sludge waste utilization technologies with the maximum use of their resource-valuable components.

After analyzing the possible methods for the disposal of CWT sludge, we have chosen a method – sorption purification of gas emissions from nitrogen and sulfur oxides using carbonate sludge.

The use of this method will provide a high rate of purification of flue gases from nitrogen oxides and sulfur oxides and a reduction in the cost of purification due to the use of dry (moisture 20 %) sludge from the chemical water treatment plant of thermal power plants as a sorbent in the adsorber.

The adsorber for cleaning flue gases from nitrogen oxides and sulfur contains a housing 1 with a fixed sorbent layer 5 placed in it, a flue gas supply pipe 2, and a purified gas outlet pipe 3.

The difference between the proposed adsorber is that a branch pipe 6 of the sorbent outlet with absorbed nitrogen and sulfur oxides is introduced into it, and as a sorbent 5, dry sludge of cold water treatment with a moisture content of 20 % is used, placed on a steel mesh 4 with a hole size of no more than 1 mm[6].

The adsorber for cleaning flue gases from nitrogen oxides and sulfur works as follows.

Flue gases enter through the nozzle 2 into the adsorber body 1. Then they pass through a fixed bed of sorbent, which is used as dry sludge of the chemical water treatment, where they are cleaned from nitrogen oxides and sulfur oxides.

Adsorber for cleaning flue gases from nitrogen oxides and sulfur

Figure 2 – Adsorber for cleaning flue gases from nitrogen oxides and sulfur
(animation: 4 fram, 6 cycles of repeating, 130 kilobytes)

When cleaning flue gases from nitrogen oxides, physical adsorption occurs, and when cleaning from sulfur oxides, the process of chemisorption [7].

The cleaned flue gases are discharged through the nozzle 3. Nozzles 2 and 3 are connected with diffusion caps, which ensure uniform distribution of gases over a fixed bed of dry sludge 5.

The spent dry sludge of the chemical water treatment plant with absorbed nitrogen and sulfur oxides is discharged through branch pipe 6 [8].

The use of this unit will provide a high rate of purification of flue gases from nitrogen oxides and sulfur oxides and a reduction in the cost of purification due to the use of dry (20 % moisture content) sludge from thermal power plants as a sorbent in the adsorber. The purification rate reaches 99 %.

Conclusion

In the course of the work, the composition of the sludge from the Starobeshevskaya TPP, the process of sludge formation from the chemical water treatment plant was considered, the optimal methods of sludge disposal from the chemical water treatment plant were analyzed, based on the physical and chemical composition of the sludge, and a sludge disposal technology was proposed as a sorption material for cleaning gas emissions from nitrogen oxides and sulfur. The use of this method will provide a high rate of purification of flue gases from nitrogen oxides and sulfur oxides and a reduction in the cost of purification due to the use of dry (moisture 20 %) sludge from the chemical water treatment plant of thermal power plants as a sorbent in the adsorber.

When writing this essay, the master's work has not yet been completed. Final completion: June 2021. The full text of the work and materials on the topic can be obtained from the author or his manager after that date.

References

  1. Зверева Э.Р. Ресурсо– энергосберегающие технологии в мазутных хозяйствах тепловых электрических станций: монография. Казань: Казан. гос. энерг. ун–т, 2010. – 184 с.
  2. Л.А. Николаева, Е.Н. Бородай Ресурсосберегающая технология утилизации шлама водоподготовки на ТЭС. Монография. – Казань.: КГЭУ, 2015. – 110 с.
  3. Классификация отходов ТЭС. – Глобальная сеть рефератов Олбест [Электронный ресурс] – Режим доступа: http://otherreferats.allbest.ru/...
  4. Фалалеев П.П. Пути повышения эффективности энергетического строительства. // Энергетическое строительство, 2016. – 150 с.
  5. Николаева Л.А., Голубчиков М.А. Очистка производственных сточных вод от нефтепродуктов модифицированными сорбционными материалами на основе карбонатного шлама // Водоснабжение и санитарная техника. – 2016. – №7. – С. 251 – 258.
  6. Николаева Л.А., Каляпина С.А. Использование шлама химводоочистки ТЭС в производстве полимерных композитов // Экология и промышленность России. – 2017. – №11. – С. 5 – 7.
  7. Николаева Л.А., Хуснутдинова А.Н. Очистка газовых выбросов предприятий химической промышленности карбонатным шламом // Экология и промышленность России. – 2018. – Т. 22. – №8. – С. 14 – 18.
  8. Вальдберг А.Ю. Процессы и аппараты защиты окружающей среды. Защита атмосферы / А.Ю. Вальдберг, Н.Е. Николайкина.– М.: Высшее образование, 2008. – 240 с.