Thread Content
This post was last edited by yinkuilin6868 on 2015-12-22 at 14:10. Safety issues related to factory layout are crucial in factory design; safety is the top priority. This paper briefly analyzes the safety requirements for each area of the factory layout. The layout of chemical plants generally adopts a zoned approach with certain spacing between areas. A factory site can generally be divided into the following six areas: process unit area ； Tank farm ； Utilities area ； Transportation and loading/unloading area Auxiliary production area ； Management area. 1 Process unit area: The processing units may be the most dangerous areas in a factory. First, the primary hazards in this area should be identified, such as toxic or flammable substances, high temperatures, high pressures, and sources of fire. These places have many mechanical devices that are prone to failure, and combined with possible human errors, they become highly dangerous. The only advantage in terms of safety is that there are usually fewer personnel in the process units. The processing units should be located at a certain distance from the factory boundaries, and they should be arranged in a concentrated manner rather than scattered. The latter helps identify the processing unit as a hazardous area, thereby preventing or reducing the passage of unrelated vehicles. Attention should be paid to the main sources of fire and the densely populated areas within the plant; due to the possibility of release of flammable or toxic substances, processing units should be located downwind of these areas. There is a risk of interaction between the process area and the main irrigation area; it is best to keep them at a considerable distance from each other. In addition to being concentrated, process units should also be arranged so that the areas are not too crowded. Since there may be a risk of interaction between different process units, a certain distance should be maintained between them. Especially in cases where the units are not part of an integrated process, it is quite possible for one unit to be operating at full capacity while a neighboring unit is being shut down for major maintenance, thereby increasing potential hazards. Sources of fire in hazardous areas, large-scale operations, the movement of machinery, and crowds of people are all matters that require special attention. Currently, in the chemical industry, the spacing between process units remains an important aspect of safety assessment. For the safety assessment of the process unit itself, important factors include: ① Operating temperature ； ②Operating pressure ； ③Type of materials in the unit ； ④Amount of material in the unit ； ⑤Type of device in the unit ； ⑥Relative investment amount per unit ； ⑦Space required for firefighting or other emergency operations. Storage containers in the 2-tank area, such as storage tanks, are devices that require special attention. Each such container is a huge reservoir of energy or toxic substances. It is wise to maintain as great a distance as possible between personnel, operating units, and storage tanks. Such containers can release large amounts of toxic or flammable substances, so they must be placed in the downwind area of the factory. As mentioned earlier, storage tanks should be located in designated areas within the factory, with clear markings indicating that they are hazardous zones, in order to minimize the presence of unauthorized vehicles in those areas. There are three basic issues regarding the layout of the tank farm: (1) the spacing between tanks ； (2) Distance between the tank and other equipment ； (3) The area required to construct a liquid retention dike. Generally, it is as follows: (1) Crushing equipment: It is installed at the bottom of the workshop, with multiple units arranged in groups, and the distance between crushing machines is greater than 800–1000 mm. (2) Cooking equipment: Arranged along the longitudinal walls of the workshop, at a distance of more than 800 mm from the walls; suspended from support beams. (3) Mashing equipment: Located between the first and second floors of the mashing workshop; the second floor serves as the operating floor. The spacing between pots is generally 3–4 m, and the equipment is placed 1 m away from the wall. (4) Fermentation equipment: The anaerobic fermentation equipment is installed indoors or in a semi-outdoor area, arranged in a straight line along the length of the workshop, or symmetrically in two or three straight lines. The distance between fermentation tanks is greater than 500 mm, the distance from them to the walls is greater than 800 mm, the distance between two rows of tanks is 1.5–2.0 m, and the distance from the tank bottoms to the ground is greater than 800 mm ； Aeration fermenters are placed indoors, arranged in a row along the length of the workshop against the walls, or in two straight lines on either side of the workshop. The distance between the tank and the wall is greater than 1000 mm; the spacing between tanks is generally greater than 1000 mm. The bottom of the tank is more than 500 mm above the ground. Closely related to these three issues are two significant hazards associated with storage tanks: one is that the tank shell may rupture, resulting in the rapid release of all its contents ； Another issue is that when a tank containing a water layer is heated above the boiling point of water, superheating of the material can occur. Just as in the case of processing units, in terms of the actual space required for the above three issues, the chemical industry still has no specific design guidelines. A sufficient safety distance should be maintained between the tank area and the offices as well as the auxiliary production areas. An adequate distance should be maintained between the tank area and the process unit area, as well as from roads. The tank area should be located in a area with a terrain level slightly lower than that of the process unit area, and must never be situated on a high slope. There are also routing issues. Each tank should be accessible via a passage on at least one side, and ideally on both opposite sides. 3 Utility Area: The utility area should be located away from the process unit area, tank farm, and other hazardous areas, so as to ensure a steady supply of water, electricity, steam, etc. in case of emergencies. The main utility pipes that enter the plant from outside should also not pass through hazardous areas; if this cannot be avoided, necessary protective measures must be taken. The factory layout should minimize the crossing of underground pipelines over roads. An important feature of pipeline configuration is the installation of loop pipelines in some devices. A failure at any point in the circuit system can cause the valve to close, isolating it and connecting the device to the rest of the system. To achieve this, it is necessary to ensure that these devices can approach the critical points of the plant from at least two directions. To enhance safety, especially in emergency situations, the pipelines of these installations must form a loop for the transmission of substances such as fire-fighting water, electricity, or steam for heating. Boiler equipment and power distribution equipment can become sources of ignition, and should be located upwind of equipment containing flammable liquids. Boiler rooms and pump stations should be located in areas of the plant where fires or explosions at other facilities cannot pose a threat. Special attention should be paid to pipelines passing above roads. The clearance under the elevated structure should provide easy access for heavy equipment such as cranes, thereby reducing the risk of collisions. Finally, the pipelines must not pass through the cofferdam area, as a fire in that area could damage the pipelines. The smoke emitted by cooling towers can impair visibility, and they should not be located near railways, roads, or other public facilities. Large cooling towers produce a lot of noise and should be located at a considerable distance from residential areas. 4 Transportation and loading/unloading area: A well-designed factory layout does not permit railway spurs to run through the plant premises; this issue can be resolved by planning the railway spur along the periphery of the factory. Similar considerations are often applied to tank trucks and their loading/unloading facilities. Spills of toxic or flammable substances may occur on the loading and unloading platforms; therefore, such facilities should be located downwind of the factory, preferably in peripheral areas. Facilities with frequent traffic of motor vehicles, such as raw material warehouses, finished product warehouses, and loading/unloading stations, shall not be located in areas that must pass through process unit zones and tank farms, and should maintain a certain safety distance from residential areas, highways, and railways. 5 Auxiliary production area: The maintenance workshop and laboratories should be located away from the process unit area and tank farm. The repair shop is a significant source of fire, and as it is also crowded with people, it should be located in the upwind area of the factory. From a functional perspective, laboratories are generally located next to other administrative facilities, but occasionally small amounts of toxic or flammable substances may be released from the laboratories into those other facilities; therefore, a direct connection between them is not appropriate. The wastewater treatment facility is the final point where toxic or flammable substances from various parts of the factory are collected, and it should be located in a remote area downwind of the factory. The safety considerations for high-temperature calcination furnaces present contradictions. As a heat source, it should be placed upwind of the factory; however, serious operational errors can cause the calcination furnace to emit a considerable amount of flammable materials, in which case it should be placed downwind of the factory. As a compromise, the calcination furnace can be placed in the side wind area of the factory. It is also a viable option to keep a certain distance from other facilities. 6 Management areas: Every factory needs certain management organs. For safety reasons, the main office should be located in the peripheral area of the factory, and as far as possible, separated from the factory’s hazardous zones. There are several reasons for this: first, sales and supply staff, as well as other individuals who need to handle affairs at the factory, do not need to enter the factory premises. Since these employees are not familiar with the nature and locations of hazards in the factory, and their usual habit of smoking inadvertently in hazardous areas could pose a threat to the safety of the factory. Secondly, the density of office staff may be the highest in the entire factory; separating these employees from hazards will improve the safety conditions of the factory. In factory layouts, there aren’t always ideal flat areas; sometimes factories have to be built in hilly regions. There are a few points worth noting: from a fire hazard perspective, the source of flammable liquids or vapors should not be located on a slope ； Low-lying areas are prone to flooding; boiler rooms, substations, pump stations, etc. should be located on higher ground ； In emergency situations, such as during flood periods, the continuous operation of these devices is essential. Storage tanks are vulnerable to damage in floods; empty tanks can float even at very low water levels, causing their connecting pipelines to break and resulting in massive leaks, thereby exacerbating the crisis. It is even necessary to consider setting up physical barrier systems to prevent the flow of liquids or the spread of fire from one plant area to another. Therefore, the presence of the following hazards must be taken into account in plant layout: ① The presence of flammable materials ； ②A heat source is present ； ③There is a source of fire present ； ④Oxygen-rich environment exists ； ⑤There is compressed material present ； ⑥Toxic substances are present ； ⑦Possibility of human error ； ⑧Probability of mechanical failure ； ⑨The movement of personnel, materials, and vehicles within the factory premises ； ⑩Due to vapor clouds reducing visibility, etc. And the designer needs to consider the following factors: ① Operating temperature ； ②Operating pressure ； ③Type of materials in the unit ； ④Amount of material in the unit ； ⑤Type of device in the unit ； ⑥Relative investment amount per unit ； ⑦Space required for firefighting or other emergency operations. This is the only way to avoid dangers as much as possible.