Desulfurizing tower outlet flue gas washing device

Abstract

The invention belongs to the technical field of desulfurization tower flue gas washing, and discloses a desulfurization tower outlet flue gas washing device which comprises an operation table. A cyclic utilization assembly is mounted on the surface of the operation table and comprises a washing tower mounted on the upper surface of the operation table, a water outlet pipe mounted on the lower surface of the operation table, a circulating pipe for cyclic utilization, a water suction pump, a water storage tank, a filter plate and an air inlet pipe; and a dismounting and cleaning assembly is mounted on the surface of the filter plate and comprises positioning strips symmetrically mounted on the surface of the filter plate, a positioning groove formed in the water storage tank, and a sealing plate and a bolt which are used for fixing. The waste water is prevented from directly entering the waste water treatment system, the recycling assembly and the dismounting and cleaning assembly are separated through the operation table, the split design is convenient to maintain, meanwhile, high-precision parts are reduced, and the production cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of flue gas scrubbing technology for desulfurization towers, specifically a flue gas scrubbing device for the outlet of a desulfurization tower. Background Technology

[0002] In industrial production, especially in industries such as power, steel, and chemicals, coal-fired boilers and industrial kilns generate large amounts of flue gas containing sulfur compounds during operation. If this sulfur-containing flue gas is directly emitted into the atmosphere, it will not only cause serious air pollution and lead to environmental problems such as acid rain, but also pose a great threat to the ecological environment and human health. Therefore, desulfurization treatment of sulfur-containing flue gas has become an indispensable environmental protection step in industrial production.

[0003] Existing flue gas scrubbing devices at the outlet of desulfurization towers mainly rely on a spray system to spray scrubbing water into the flue gas during operation. The contact between the scrubbing water and the flue gas dissolves or adsorbs dust, residual desulfurizing agent particles, and some harmful gases, thereby purifying the flue gas. However, in practical applications, these devices generally suffer from a key problem: the wastewater generated during the scrubbing process cannot be repeatedly recycled.

[0004] Existing technology, patent CN110102164A, discloses a wet desulfurization process for high-sulfur concentration flue gas. Its structure includes a first desulfurization tower, on which are installed a smoke extraction pipe, a first chimney, a connecting pipe, a sulfur dioxide detector, a filter plate, and a wastewater recovery tank. The smoke extraction pipe is fixedly connected to the lower left of the first desulfurization tower, the first chimney is fixedly connected to the upper left of the first desulfurization tower, the connecting pipe is fixedly connected to the upper end of the first desulfurization tower, the sulfur dioxide detector is fixedly connected to the top inside the first desulfurization tower, and the filter plate is fixedly connected to the bottom inside the first desulfurization tower. This invention reduces the probability of water waste and avoids sulfur dioxide in the flue gas being mixed in with the flue gas and emitted into the air. However, the device has a complex structure, high cost, and a high maintenance cost due to its integrated design. Summary of the Invention

[0005] To address the problems of complex structure, high cost, integrated design, and high maintenance cost mentioned in the background art, the present invention provides a desulfurization tower outlet flue gas scrubbing device.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a flue gas scrubbing device for desulfurization tower outlet, comprising an operating platform, wherein the operating platform is equipped with a recycling component, the recycling component comprising a scrubbing tower, an outlet pipe, a circulation pipe, a pump, and a storage tank, wherein the scrubbing tower is located on the upper surface of the operating platform, the outlet pipe is located on the lower surface of the operating platform, one end of the circulation pipe is connected to the outer surface of the scrubbing tower, the other end of the circulation pipe is connected to the pump, the pump is located at the outlet of the storage tank, and the inlet of the storage tank is connected to the outlet pipe.

[0007] Furthermore, the recycling component is connected to the flue gas outlet of the desulfurization tower via an air inlet pipe.

[0008] Furthermore, the water storage tank is equipped with a filter plate, which has two or more filter holes.

[0009] Furthermore, it also includes a disassembly and cleaning assembly, which includes a positioning strip, a positioning groove, a sealing plate, and a bolt. The positioning strip is slidably connected to the positioning groove, which is located inside the water tank. The end of the positioning groove is fixedly connected to the inner side of the sealing plate, and the bolt is threadedly connected to a threaded hole on the surface of the sealing plate.

[0010] Furthermore, the washing tower is equipped with a spray mechanism that communicates with the circulation pipe.

[0011] Furthermore, the water outlet pipe, the circulation pipe, and the air inlet pipe are equipped with control valves.

[0012] Furthermore, the water storage tank is equipped with a water level monitoring mechanism.

[0013] Furthermore, the water level monitoring mechanism includes a water level sensing module, a float, and a T-shaped block. The water level sensing module is embedded in the water storage tank. The float is attached to the water level sensing module through an embedded trigger block. The T-shaped block is symmetrically arranged on the inner side of the float and is slidably connected to a T-shaped groove provided inside the water storage tank.

[0014] Furthermore, the inlet of the water outlet pipe is higher than the bottom of the washing tower.

[0015] Furthermore, the water storage tank is provided with threaded holes.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] 1. This invention separates the recycling component and the disassembly and cleaning component through the operating table. The split design facilitates maintenance and reduces the number of high-precision parts, thereby reducing production costs.

[0018] 2. A complete wastewater recycling chain is formed by the washing tower, effluent pipe, circulation pipe, water pump, water storage tank and filter plate in the recycling components. The wastewater after washing can flow back to the water storage tank through the effluent pipe, and after being filtered by the filter plate, it is pumped back to the washing tower for reuse through the circulation pipe. This avoids the wastewater from directly entering the wastewater treatment system, so that water resources can be effectively utilized and the consumption of fresh water can be greatly reduced.

[0019] 3. By disassembling and cleaning the components, the sliding engagement of the positioning strip and the positioning groove provides guidance for the filter plate, preventing filter plate misalignment during installation and resulting in filter hole blockage or seal failure. At the same time, the sliding structure restricts the displacement of the filter plate in the water storage tank, ensuring that the filter plate remains stable under the impact of wastewater, guaranteeing stable filtration effect. It can seal the gap between the filter plate and the water storage tank, preventing unfiltered wastewater from flowing into the lower part of the water storage tank through the gap, ensuring that all wastewater is filtered. It also prevents the leakage of washing water in the water storage tank due to poor sealing, reducing water waste and environmental risks, and allows for convenient disassembly, replacement, or cleaning of the filter plate.

[0020] 4. The water level monitoring mechanism can monitor and process the water level inside the water storage tank, so as to drain water in a timely manner and maintain the current circulation state.

[0021] 5. There is a height difference between the water inlet of the outlet pipe and the scrubbing tower. The accumulated spray water can increase the time in the scrubbing tower, thereby improving the efficiency of flue gas scrubbing. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0023] Figure 2 This is a schematic diagram of the filter plate of the present invention when it is opened;

[0024] Figure 3 This is a schematic diagram of the structure of the recycling component of the present invention;

[0025] Figure 4 This is a schematic diagram of the internal structure of the washing tower of the present invention;

[0026] Figure 5 This is a schematic diagram of the structure of the filter plate and positioning strip of the present invention;

[0027] Figure 6 This is a schematic diagram of the water level monitoring mechanism of the present invention.

[0028] In the diagram: 1. Control panel; 2. Recycling component; 21. Scrubbing tower; 22. Outlet pipe; 23. Circulation pipe; 24. Water pump; 25. Water storage tank; 26. Filter plate; 27. Air inlet pipe; 28. Water level monitoring mechanism; 281. Water level sensor module; 282. Float; 283. T-block; 3. Disassembly and cleaning component; 31. Positioning strip; 32. Positioning groove; 33. Sealing plate; 34. Bolt. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1, Reference Figures 1-6 .

[0031] A flue gas scrubbing device for desulfurization tower outlet includes an operating platform 1. The operating platform 1 is equipped with a recycling component 2. The recycling component 2 includes a scrubbing tower 21, a water outlet pipe 22, a circulation pipe 23, a water pump 24, and a water storage tank 25. The scrubbing tower 21 is located on the upper surface of the operating platform 1, the water outlet pipe 22 is located on the lower surface of the operating platform 1, one end of the circulation pipe 23 is connected to the outer surface of the scrubbing tower 21, and the other end of the circulation pipe 23 is connected to the water pump 24. The water pump 24 is located at the outlet of the water storage tank 25, and the inlet of the water storage tank 25 is connected to the water outlet pipe 22.

[0032] The scrubbing tower 21 is equipped with a spraying mechanism that communicates with the circulation pipe 23. The spraying mechanism is a spray head located at the outlet of the circulation pipe 23. The spray head has a micro-pressure function, which can atomize the water flow and expand the spraying area.

[0033] One end of the air inlet pipe 27 is connected to the air inlet of the washing tower 21, and one end of the water outlet pipe 22 passes through the operating table 1 and is connected to the washing tower 21. The water storage tank 25 is installed on the bottom surface of the operating table 1.

[0034] The other end of the inlet pipe 27 is connected to the flue gas outlet of the desulfurization tower, which clarifies the connection between the inlet pipe 27 and the flue gas outlet of the desulfurization tower.

[0035] The recycling component 2 is connected to the flue gas outlet of the desulfurization tower through the air inlet pipe 27. The water storage tank 25 is equipped with a filter plate 26, which has two or more filter holes. The component also includes a disassembly and cleaning component 3, which includes a positioning strip 31, a positioning groove 32, a sealing plate 33, and a bolt 34. The positioning strip 31 is slidably connected to the positioning groove 32. The positioning groove 32 is located inside the water storage tank 25. The end of the positioning groove 32 is fixedly connected to the inner side of the sealing plate 33. The bolt 34 is threadedly connected to the threaded hole opened on the surface of the sealing plate 33.

[0036] The positioning strip 31 is slidably connected within the positioning groove 32. The sealing plate 33 is installed at one end of the filter plate 26 and fits against the water storage tank 25. The sliding cooperation between the positioning strip 31 and the positioning groove 32 provides guidance for the filter plate 26, preventing filter hole blockage or sealing failure caused by filter plate 26 shifting during installation. At the same time, the sliding structure restricts the displacement of the filter plate 26 within the water storage tank 25, ensuring that the filter plate 26 remains stable under the impact of wastewater, guaranteeing stable filtration effect. It can seal the gap between the filter plate 26 and the water storage tank 25, preventing unfiltered wastewater from flowing into the lower half of the water storage tank 25 through the gap, ensuring that all wastewater is filtered. It also prevents the washing water in the water storage tank 25 from leaking due to poor sealing, reducing water waste and environmental risks, and facilitating the disassembly, replacement, or cleaning of the filter plate 26.

[0037] The surface of the filter plate 26 is equipped with a cleaning and disassembly assembly 3, which includes positioning strips 31 symmetrically installed on the surface of the filter plate 26, positioning grooves 32 opened inside the water storage tank 25, sealing plates 33 and bolts 34 for fixing, positioning strips 31 slidingly connected in the positioning grooves 32, and sealing plates 33 installed on one side of the filter plate 26 and in contact with the water storage tank 25.

[0038] The water tank 25 is provided with a threaded hole, and the bolt 34 is threaded into the threaded hole on the surface of the sealing plate 33. One end of the bolt 34 passes through the sealing plate 33 and is threaded into the threaded hole on the surface of the water tank 25. The threaded connection of the bolt 34 can provide a stable locking force to tightly press the sealing plate 33 onto the surface of the water tank 25.

[0039] One end of the air inlet pipe 27 is connected to the air inlet of the washing tower 21, and one end of the water outlet pipe 22 passes through the operating platform 1 and is connected to the washing tower 21. The water storage tank 25 is installed on the bottom surface of the operating platform 1, and the water outlet pipe 22 is connected to the water storage tank 25. The water pump 24 is installed at the water outlet of the water storage tank 25. The circulation pipe 23 is connected to the surface of the washing tower 21, and one end of the circulation pipe 23 is connected to the water pump 24. The filter plate 26 is set inside the water storage tank 25. The washing tower 21, water outlet pipe 22, circulation pipe 23, water pump 24, water storage tank 25 and filter plate 26 in the recycling component 2 form a complete wastewater circulation link. The wastewater after washing can flow back to the water storage tank 25 through the water outlet pipe 22. After being filtered by the filter plate 26, it is pumped by the water pump 24 and transported back to the washing tower 21 for reuse through the circulation pipe 23, which greatly reduces the consumption of fresh water.

[0040] The filter plate 26 is located in the upper part of the water storage tank 25, and multiple filter holes are evenly opened on the surface of the filter plate 26 so that the return wastewater can come into contact with the filter plate 26 and must completely pass through the filter plate 26 before entering the lower part of the water storage tank 25, ensuring that solid pollutants such as dust and desulfurizing agent particles are fully intercepted.

[0041] When the filter plate 26 has been used for a period of time and the surface has accumulated too many solid pollutants, resulting in a decrease in filtration efficiency, stop the device operation, close all control valves, unscrew the bolt 34 in the threaded hole on the surface of the sealing plate 33. One end of the bolt 34 passes through the sealing plate 33 and is threaded into the threaded hole in the water storage tank 25. Push the sealing plate 33 to move the filter plate 26 along the positioning groove 32, so that the positioning strip 31 is disengaged from the positioning groove 32. The filter plate 26 can then be removed from the water storage tank 25. The removed filter plate 26 can be cleaned or replaced. After removing the surface pollutants, the entire water can also be replaced. Use an external water pump to pump out all the water inside for replacement. Slide the positioning strip 31 of the filter plate 26 back into the positioning groove 32 of the water storage tank 25 so that the sealing plate 33 fits into the water storage tank 25. Tighten the bolt 34 to fix it, completing the maintenance of the filter plate 26 and ensuring the subsequent filtration effect.

[0042] Example 2, reference Figures 1-6 .

[0043] A flue gas scrubbing device for desulfurization tower outlet includes an operating platform 1. The operating platform 1 is equipped with a recycling component 2. The recycling component 2 includes a scrubbing tower 21, a water outlet pipe 22, a circulation pipe 23, a water pump 24, and a water storage tank 25. The scrubbing tower 21 is located on the upper surface of the operating platform 1, the water outlet pipe 22 is located on the lower surface of the operating platform 1, one end of the circulation pipe 23 is connected to the outer surface of the scrubbing tower 21, and the other end of the circulation pipe 23 is connected to the water pump 24. The water pump 24 is located at the outlet of the water storage tank 25, and the inlet of the water storage tank 25 is connected to the water outlet pipe 22. The water outlet pipe 22, the circulation pipe 23, and the air inlet pipe 27 are equipped with control valves.

[0044] Control valves are installed on the surfaces of the water outlet pipe 22, the circulation pipe 23 and the air inlet pipe 27. The flue gas flow rate of the air inlet pipe 27, the wastewater return / transport rate of the water outlet pipe 22 and the circulating water flow rate of the circulation pipe 23 can be adjusted by controlling the valves to adapt to different flue gas concentrations and washing requirements.

[0045] The water storage tank 25 is equipped with a water level monitoring mechanism 28, which includes a water level sensing module 281, a float 282, and a T-shaped block 283. The water level sensing module 281 is embedded in the water storage tank 25. The float 282 is attached to the water level sensing module 281 through an embedded trigger block. The T-shaped block 283 is symmetrically arranged on the inner side of the float 282 and is slidably connected to the T-shaped groove provided in the water storage tank 25.

[0046] The water level monitoring mechanism 28 includes a water level sensing module 281 embedded inside the water storage tank 25. A float 282 is provided inside the water storage tank 25. T-shaped blocks 283 are symmetrically installed on the surface of the float 282. The T-shaped blocks 283 are slidably connected in the T-shaped grooves opened inside the water storage tank 25. A trigger block is embedded inside the float 282, and this trigger block is in contact with the water level sensing module 281, thereby enabling the monitoring and processing of the water level inside the water storage tank 25, so that water can be discharged in time to maintain the current circulation state.

[0047] The water tank 25 contains water at a pre-set initial water level. The float 282 suspends at the corresponding height according to the water level. The T-shaped block 283 on its surface is embedded in the T-shaped groove inside the water tank 25 and remains stable. The T-shaped groove restricts the lateral displacement of the float 282. The trigger block inside the float 282 initially engages with the water level sensing module 281 inside the water tank 25, transmitting the current water level reference signal to the device control system. When the water level in the water tank 25 is replenished by wastewater, such as washing wastewater discharged from the desulfurization tower 21 flowing into the tank through the outlet pipe 22, or... Because of the cyclic use, when the water pump 24 pumps water down through the circulation pipe 23, the float 282 rises and falls synchronously with the water level. The T-shaped block 283 slides directionally along the T-shaped groove, causing the contact position between the trigger block inside the float 282 and the water level sensing module 281 to change. By contacting different sensing areas of the water level sensing module 281, the trigger block converts the physical states such as low water level, medium water level, and high water level into corresponding electrical signals. These signals are transmitted to the core control system of the device in real time. After receiving the signal, the control system executes the corresponding control commands.

[0048] Example 3, reference Figures 1-6 .

[0049] A flue gas scrubbing device for desulfurization tower outlet includes an operating platform 1. The operating platform 1 is equipped with a recycling component 2, which includes a scrubbing tower 21, an outlet pipe 22, a circulation pipe 23, a water pump 24, and a water storage tank 25. The scrubbing tower 21 is located on the upper surface of the operating platform 1, and the outlet pipe 22 is located on the lower surface of the operating platform 1. One end of the circulation pipe 23 is connected to the outer surface of the scrubbing tower 21, and the other end of the circulation pipe 23 is connected to the water pump 24. The water pump 24 is located at the outlet of the water storage tank 25, and the inlet of the water storage tank 25 is connected to the outlet pipe 22. There is a height difference between the outlet pipe 22 and the scrubbing tower 21, and the outlet pipe 22 is higher than the scrubbing tower 21, while the inlet of the outlet pipe 22 is higher than the bottom of the scrubbing tower 21.

[0050] Working principle: Ensure that the washing tower 21, water tank 25, water pump 24 and other recycling components 2 on the operating table 1 are installed securely. The filter plate 26 is slidably connected to the positioning groove 32 of the water tank 25 through the positioning strip 31 of the disassembly and cleaning component 3. The sealing plate 33 is attached to the water tank 25, and the bolt 34 passes through the sealing plate 33 and is threaded in the threaded hole of the water tank 25, ensuring that the filter plate 26 is stable and the water tank 25 is sealed.

[0051] Close the control valves on the surface of the water outlet pipe 22, circulation pipe 23 and air inlet pipe 27, and inject sufficient fresh washing water into the water tank 25 through the water inlet. Stop injecting water after the water level reaches the preset height.

[0052] Open the control valve on the surface of the inlet pipe 27. The flue gas from the desulfurization tower is connected to the flue gas outlet of the desulfurization tower at one end through the inlet pipe 27, and enters the interior of the scrubbing tower 21 through the inlet of the scrubbing tower 21 to begin the deep purification process.

[0053] Open the control valve on the surface of the water outlet pipe 22. One end of the water outlet pipe 22 passes through the operating platform 1 and is connected to the scrubbing tower 21, while the other end is connected to the water storage tank 25. The washing water in the water storage tank 25 is transported to the scrubbing tower 21. The scrubbing tower 21 atomizes or sprays the washing water through a spray structure, so that the washing water comes into full contact with the incoming flue gas. By utilizing the dissolving and adsorption properties of water, residual dust, unreacted desulfurizing agent particles, and a small amount of harmful gases in the flue gas are removed, thus completing the deep purification of the flue gas. Since there is a height difference between the inlet of the water outlet pipe 22 and the scrubbing tower 21, the sprayed water accumulates at the bottom of the scrubbing tower 21 after spraying. As it accumulates, when the water level reaches the inlet of the water outlet pipe 22, the sprayed water flows downward along the water outlet pipe 22. The accumulated sprayed water can increase the time in the scrubbing tower 21, thereby improving the efficiency of flue gas scrubbing.

[0054] The wastewater, carrying pollutants, flows back to the storage tank 25 through the outlet pipe 22. The storage tank 25 is installed on the bottom of the operating table 1 and is connected to the outlet pipe 22. It enters the wastewater recycling stage. The wastewater flowing into the storage tank 25 first comes into contact with the filter plate 26 located in the upper part of the storage tank 25. Multiple filter holes are evenly opened on the surface of the filter plate 26, which can intercept solid pollutants such as dust and desulfurizing agent particles in the wastewater. The filtered clean water falls into the lower part of the storage tank 25, realizing solid-liquid separation and laying the foundation for wastewater recycling.

[0055] When the filtered clean water in the lower half of the water storage tank 25 reaches a certain volume, the water pump 24 installed at the outlet of the water storage tank 25 is started. At the same time, the control valve on the surface of the circulation pipe 23 is opened. The water pump 24 draws out the filtered clean water from the water storage tank 25 and transports it to the circulation pipe 23 on the surface of the scrubbing tower 21 through one end connected to the water pump 24 and the other end connected to the scrubbing tower 21. The water is then sprayed again through the spray structure and used for flue gas scrubbing, forming a closed loop of wastewater recycling of "washing-recovery-filtration-rewashing", reducing the consumption of fresh water and reducing water waste.

[0056] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flue gas scrubbing device for the outlet of a desulfurization tower, comprising an operating table (1), characterized in that: The operating platform (1) is equipped with a recycling component (2), which includes a washing tower (21), an outlet pipe (22), a circulation pipe (23), a water pump (24), and a water storage tank (25). The washing tower (21) is located on the upper surface of the operating platform (1), the outlet pipe (22) is located on the lower surface of the operating platform (1), one end of the circulation pipe (23) is connected to the outer surface of the washing tower (21), and the other end of the circulation pipe (23) is connected to the water pump (24). The water pump (24) is located at the outlet of the water storage tank (25), and the inlet of the water storage tank (25) is connected to the outlet pipe (22).

2. The flue gas scrubbing device at the outlet of a desulfurization tower according to claim 1, characterized in that: The recycling component (2) is connected to the flue gas outlet of the desulfurization tower through the air inlet pipe (27).

3. The flue gas scrubbing device at the outlet of a desulfurization tower according to claim 1, characterized in that: The water storage tank (25) is equipped with a filter plate (26) inside, and the filter plate (26) has two or more filter holes.

4. The flue gas scrubbing device at the outlet of a desulfurization tower according to claim 1, characterized in that: It also includes a disassembly and cleaning assembly (3), which includes a positioning strip (31), a positioning groove (32), a sealing plate (33), and a bolt (34). The positioning strip (31) is slidably connected to the positioning groove (32), the positioning groove (32) is located inside the water tank (25), the end of the positioning groove (32) is fixedly connected to the inner side of the sealing plate (33), and the bolt (34) is threadedly connected to a threaded hole opened on the surface of the sealing plate (33).

5. The flue gas scrubbing device at the outlet of a desulfurization tower according to claim 1, characterized in that: The washing tower (21) is equipped with a spraying mechanism that communicates with the circulation pipe (23).

6. The flue gas scrubbing device at the outlet of a desulfurization tower according to claim 1, characterized in that: The water outlet pipe (22), the circulation pipe (23) and the air inlet pipe (27) are equipped with control valves.

7. The flue gas scrubbing device at the outlet of a desulfurization tower according to claim 1, characterized in that: The water storage tank (25) is equipped with a water level monitoring mechanism (28).

8. The flue gas scrubbing device at the outlet of a desulfurization tower according to claim 7, characterized in that: The water level monitoring mechanism (28) includes a water level sensing module (281), a float (282), and a T-shaped block (283). The water level sensing module (281) is embedded in the water storage tank (25). The float (282) is attached to the water level sensing module (281) through an embedded trigger block. The T-shaped block (283) is symmetrically arranged on the inner side of the float (282). The T-shaped block (283) is slidably connected to the T-shaped groove provided in the water storage tank (25).

9. The flue gas scrubbing device at the outlet of a desulfurization tower according to claim 1, characterized in that: The inlet of the outlet pipe (22) is higher than the bottom of the washing tower (21).

10. A desulfurization tower outlet flue gas scrubbing device according to claim 1, characterized in that: The water storage tank (25) is provided with a threaded hole.

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