Application of zero discharge technology of desulfurization wastewater in Yangdian Company

introduction

The impurities in the desulfurization wastewater of thermal power plants come from flue gas and limestone used for desulfurization, mainly including suspended solids, supersaturated sulfites, sulfates and heavy metals, many of which are the first-class pollutants required to be controlled in the national environmental protection standards. The purpose of the zero-emission project of spray drying of desulfurization wastewater of #6 and #7 units (2×330Mw) of Jiangsu Huadian Yangzhou Power Generation Co., Ltd. is to explore the way to treat the maximum amount of desulfurization wastewater under the premise of ensuring the safety of the unit through a series of tests on spray drying of desulfurization wastewater in the bypass flue, and optimize the overall treatment process route of desulfurization wastewater by studying the impact on the quality of ash and gypsum, so as to find an economical and technically advanced way to reduce desulfurization wastewater for the group's coal-fired units.

1. Process route for desulfurization wastewater treatment

(1) Desulfurization wastewater and water treatment reclaimed water and fine treatment reclaimed water from chemical water workshop: The water treatment reclaimed water from chemical water workshop is led out from the pipeline connected to the main plant wastewater treatment workshop to the concentrator clarifier: The fine treatment reclaimed water is led out from the pipeline connected to the main plant wastewater treatment workshop to the concentrator clarifier. The reclaimed wastewater stored in the concentrator clarifier is pumped to the triple box of the desulfurization wastewater treatment system for pH adjustment and then flows into the clean water tank. The desulfurization wastewater is also pH adjusted through the triple box and then flows into the clean water tank. After pH adjustment, the wastewater in the clean water tank is transported to the wastewater buffer tank through the clean water pump, and then pumped to the wastewater buffer tank through the wastewater buffer tank. The wastewater in the wastewater buffer tank flows into the drying tower by gravity, and is atomized into fine droplets by a high-speed rotating atomizer. It is then fully heat exchanged with the hot flue gas led out from the denitrification outlet. The heat of the flue gas is used to instantly dry the desulfurization wastewater. The large particles of solid matter produced by drying are discharged from the discharge port at the bottom of the spray drying tower. The small particles of solid matter are dried by the spray drying tower and returned to the electrostatic precipitator inlet for treatment.

(2) Reverse osmosis concentrate from the chemical water treatment workshop: The reverse osmosis concentrate is pumped into the chemical water treatment neutralization tank for storage, and then pumped into the process water tank of the desulfurization system through a reverse osmosis water pump to be used as process make-up water for the existing desulfurization system.

This project is a scientific and technological project, which will establish an application engineering test platform for the research of zero-emission spray drying of desulfurized wastewater. During the implementation of the project, the impact on the original unit system, equipment and pipeline layout should be minimized, and the project implementation time should be reasonable, and it should be completed as much as possible within the planned maintenance period of the unit.

2Spray drying process system

As shown in Figure 1, the process system mainly consists of the following parts: flue gas system, drying tower system, wastewater feeding system, process water system, industrial water system, compressed air system, and ash conveying system.

2.1 Flue gas system

The flue gas system mainly includes flue, damper door, expansion joint, etc. The flue gas is led out from the denitrification outlet to the air preheater section, and the high-temperature flue gas is merged into the spray drying tower. The flue gas dried by the spray drying tower returns to the flue on the front side of the MGGH.

2.2 Spray Drying Tower System

The spray tower system mainly includes a drying tower and its ancillary equipment.

2.2.1 Spray Drying Tower

Each boiler in this project is equipped with a spray drying tower, and a total of two are configured. The dimensions of the drying tower are: inner diameter 8.5m, cylinder height 16m, and total height of about 36.5m. The spray drying tower consists of two parts: the upper and lower parts of the cylinder and the cone. Hot flue gas and wastewater enter the drying tower from the top of the tower. The dried flue gas leaves the drying tower from the upper part of the cone, and large particles of solid matter enter the warehouse pump from the bottom of the tower. The tower body of the drying tower is made of carbon steel, and the tower body is supported by an integral steel frame. The interior is an empty tower structure. A maintenance room is set at the top of the tower, and a maintenance lifting device is set. A 4.5m aisle is reserved at the bottom of the tower. The drying tower is equipped with a certain number of manhole doors and observation holes. The manhole doors and observation holes are completely smoke-free, and walkways or platforms are set near them. The outer surface of the drying tower needs to be insulated. The thickness of the insulation layer is 200mm (aluminum silicate wool), and the outer skin is a color steel plate (0.75mm).

2.2.2 Rotary Atomizer

The rotary atomizer is the core component of the entire spray drying system. The basic principle of the rotary atomizer is that when the desulfurized wastewater after quenching and conditioning is pumped to the high-speed rotating atomizing disk, it is stretched into a thin film or pulled into filaments (depending on the rotation speed and the amount of slurry) due to the centrifugal force, and then breaks and disperses into droplets at the edge of the atomizing disk (the size of the droplets depends on the rotation speed and the amount of slurry). Each atomizer in this project is equipped with a 45kw dual-frequency motor and a frequency converter. The speed of the atomizer is 10000~13000r/min, which can be adjusted according to the frequency converter. The average diameter of the sprayed droplets is 10~60μm. In order to ensure that the incoming liquid can be distributed smoothly and evenly from the liquid supply pipe to the atomizing disk, a special liquid distribution part is installed near the atomizing disk at the lower end of the main shaft. The atomizing disk is a disc with a diameter of 250mm. The material of the atomizer: the atomizing disk is made of ceramic-lined Hastelloy, the protective cover is 304 stainless steel, and the liquid inlet pipe is made of titanium tube. The atomizer is equipped with oil circuit cooling and circulating water cooling system.

2.2.3 Flue gas distributor

The flue gas distributor is set at the top of the spray drying tower. Its function is to make the hot flue gas for drying evenly enter the drying tower, effectively mix with the atomized droplets, and evaporate the water quickly. The flue gas distributor is equipped with a wind guide plate with a certain angle to control the flow direction of the hot flue gas, so that the mixing of the droplets and the hot flue gas meets the appropriate requirements and improves the atomization efficiency. The flue gas distributor adopts the form of a volute and is made of 304 stainless steel.

2.3 Desulfurization wastewater feeding system

The core of the spray drying process technology is the rotary atomizer, which has good adaptability to various water qualities. The desulfurization wastewater does not need to be pretreated, and the pH value can be adjusted to 9-10. The original desulfurization wastewater treatment system only needs to add a lime milk system, and the original flocculation, sedimentation, plate and frame filter press, etc. do not need to be operated, which can save operating costs.

The specific process is as follows: the treated recycled water from the chemical water workshop is led out from the pipeline connected to the main plant's wastewater treatment workshop to the concentrator and clarifier: the finely treated recycled water is led out from the pipeline connected to the main plant's wastewater treatment workshop to the concentrator and clarifier, the regenerated wastewater stored in the concentrator and clarifier is pumped to the triple box of the desulfurization wastewater treatment system for pH adjustment and then flows into the clean water tank, the desulfurization wastewater is also pH adjusted through the triple box and then flows into the clean water tank, the wastewater in the clean water tank is transported to the wastewater buffer tank through the clean water pump, and then pumped to the wastewater buffer tank through the wastewater buffer tank, the wastewater in the wastewater buffer tank flows by gravity to the drying tower for drying treatment.

Description of the modification of the original desulfurization wastewater system: (1) The flocculation and sedimentation links in the original wastewater system will be discontinued for this wastewater zero discharge project; (2) The original acid addition link will be discontinued for this project; (3) The plate and frame filter press, sludge circulation pump, and sludge transfer pump will be discontinued for this project; (4) The original concentrator clarifier is used to store the water treatment recycled water and fine treatment recycled water of the water treatment workshop; (5) For the modification of other pipelines, please refer to the corresponding pipeline drawings.

2.4 Utility Engineering System

The utility system includes process water system, industrial water system, compressed air system and ash conveying system. The process water system is used as system pipeline flushing water and pump sealing water (pump sealing water cannot enter the wastewater pit to prevent it from entering the system). The industrial water system is used as cooling water for the oil circuit of the atomizer. The compressed air system includes instrument compressed air and miscellaneous compressed air. The compressed air of the ash conveying system uses miscellaneous compressed air, and the compressed air for cooling the atomizer uses instrument compressed air (instrument compressed air is connected to the pipeline interface behind the denitrification instrument air tank). Ash conveying system: After the wastewater is dried in the drying tower, part of the solid salt and dust entrained in the flue gas flow into the main flue with the flue gas, and the other part flows to the bottom of the tower and is transported to the existing electrostatic precipitator system through pneumatic ash conveying. Outlet: The silo pump outlet is connected to the outlet main pipe of the electrostatic precipitator ash conveying system.