What is split-range control

It’s best to refine the question further and make it more comprehensive. It’s best to ask your supervisor; after all, it’s the person who created the problem who should solve it. Don’t forget that he is a person just like you; it is his duty to teach you skills.

What does split-range control generally mean in hydrogenation?

Meaning: One regulator controls two or several control valves. This is the most common control method in chemical process control.

In hydrogenation, split-stage control simply refers to the controlled regulation of pressure in the storage tank in stages. Two control valves, A and B, are installed on the top of the tank. Valve A has an opening range of 50 to 0, and it is used to inflate the tank; valve B has an opening range of 50 to 100, and it is used to release pressure from inside the tank. (A valve opening of 50 represents the 0 point in actual operation; this means that both valves A and B are fully closed. Values of 0 and 100 indicate that both valves are fully open. This setting needs to be adjusted by the instrumentation personnel.) During operation, a constant pressure value must be set inside the tank. When the pressure inside the tank exceeds this set value, valve B gradually opens from 50 to 100%, until the pressure inside the tank reaches the set value. When the pressure inside the tank falls below the set value, valve A activates and opens gradually from 50 to 0, filling the tank with air until the pressure reaches the set value.

This post was last edited by A window that won’t close_KEIQ on 2018-4-20 at 15:40. Section 6: Distributed Control Systems 6.1 Overview In feedback control systems, it is usual for the output of a single controller to control only one control valve. In a distributed control system, the output of one controller can simultaneously control two or even more control valves. Here, the controller’s output signal is divided into several signal range segments, with each segment being used to control one control valve. The block diagram of the split-range control system is shown in Figure 5-34. file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image002.jpg In a distributed control system, the segmentation of the controller’s output signals is generally achieved by valve positioners attached to the control valves. The annoyance locator is equivalent to an amplifier with a variable gain factor, and its zero point can be adjusted. In split-range control systems, regarding the opening and closing mode of control valves, they can be divided into two categories: one category involves two control valves that operate in conjunction; that is, as the output signal from the controller (i.e., the valve pressure) increases, both control valves either open further or close partially. Its operating process is shown in Figure 5-35, where Figure (a) represents the case of a gas-open valve, and Figure (b) represents the case of a gas-close valve. Another type involves two control valves operating in opposite directions; that is, as the controller’s output signal increases or decreases, one control valve opens while the other closes, as shown in Figure 5-36. In figure (a), A is a air-operated valve. B represents the case of the valve being open. Figure (b) shows the case where A is a gas-open valve and B is a gas-close valve. file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image004.jpg The choice between concurrent or sequential operation of the directional control valve should be determined based on the actual requirements of the production process. 6.2 Applications of proportional control 1. Used to expand the adjustable range of control valves. Sometimes, the production process requires a wide range of flow rate variations, but the adjustable range of control valves is limited (for domestically produced plug control valves, the adjustable range is R=30). If a single control valve is used, the difference between the maximum and minimum flow rates that can be controlled cannot be too large, which fails to meet the requirement for large fluctuations in flow rate in production. At this point, a split-control scheme using two control valves in parallel can be considered. For example, the steam generated by the boiler has a pressure of 10 Mpa, which is high-pressure steam; whereas what is needed in production is medium-pressure steam with a pressure of 4 Mpa to maintain pressure balance. When selecting the diameter of the control valve, it is necessary to choose a large diameter in order to meet the steam supply requirements under high loads. However, under normal conditions, such a large amount of steam is not required, which necessitates closing the valve. In other words, under normal conditions, the control valve operates only at a small opening degree. When the large valve operates at a low opening degree, in addition to the distortion of its valve characteristics, noise and oscillations are likely to occur, which deteriorates the control performance and reduces the quality of control. To resolve this conflict, two control valves can be used to form a split-control scheme, as shown in Figure 5-37. In this proportional control, two control valves, A and B, are used (assuming that both are selected as air-operated valves based on the process requirements). Among them, valve A moves from fully closed to fully open when the controller output pressure is between 20 and 100 kPa. Under normal conditions, that is, at low load, valve B remains closed, and control is achieved solely through changes in the opening degree of valve A. Under heavy load, even with valve A fully open, the required amount of steam cannot be met, and the pressure in the medium-pressure steam pipeline still does not reach the specified value. As a result, the output of the reactive pressure controller PC increases, exceeding 60 kPa, which causes valve B to open as well in order to compensate for the insufficient steam supply. 2. It is used to control two different media in order to meet the requirements of industrial production. In some chemical reactions that take place on a batch basis, once the reactants are introduced into the equipment, heat must be supplied to them in order to reach the reaction temperature. Once this temperature is reached, heat is released as the chemical reaction proceeds. If this heat is not removed in a timely manner, the reaction will become increasingly intense, posing a risk of explosion. To this end, a split-control system as shown in Figure 5-38 can be designed. In this system, two control valves, A and B, are used to separately control cold water and steam, two different media, in order to meet the process requirements for cooling and heating. In the diagram, the temperature controller TC is set to a reactive mode; the cold water control valve A is of the air-shut type, while the steam control valve is of the air-open type. The split points for these two valves are as shown in the diagram. 4. As a measure for ensuring production safety, different control methods need to be employed for safety reasons, and in such cases a split-control scheme can be used. To maintain a stable nitrogen sealing pressure in the storage tank, the split-control scheme shown in Figure 5-40 can be applied. file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image010.gif In this scheme, valve A is of the air-open type and valve B is of the air-shut type; their split-point characteristics are shown in Figure 5-41. file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image012.jpg 6.3 Can be divided into several issues related to control: (1) The flow characteristics of the control valve must be selected appropriately. Because at the point where the two valves meet, the amplification factor of the control valve may change abruptly, resulting in a sharp change in slope on the characteristic curve; this is particularly important when control valves of different sizes are connected in parallel. The situation is even worse if both control valves have a linear characteristic, as shown in Figure 5-42(a). If logarithmic characteristic control valves are used and the signal overlap is reduced by a small amount, the situation will improve, as shown in Figure 5-42(b). file:///C:/Users/ccmh/AppData/Local/Temp/msohtmlclip1/01/clip_image014.jpg (2) When large valves are connected in parallel, the leakage rate of the larger valve cannot be ignored; otherwise, the advantage of expanding the adjustable range cannot be fully utilized. When the leakage rate of the large valve is high and the minimum flow rate of the system is large, the system’s minimum flow capacity is no longer equal to that of the small valve. (3) A split-range control system is essentially a simple control system; therefore, the selection of the controller and parameter tuning can be handled using the methods applicable to simple control systems. However, during operation, if the characteristics of the two control channels differ – that is, if the characteristics of the generalized objects are different – the controller parameters cannot satisfy the requirements of both different object characteristics simultaneously. In such cases, it is necessary to take into account the characteristics of the controlled object under normal conditions and adjust the controller parameters accordingly. The operating requirements for the other valve need only be within the limits permitted by the process.

The answer on floor 5 was quite detailed: pressure was continuously added while simultaneously being released, in order to maintain a stable pressure at the top of the tank

The output signal of the controller is segmented; when the pressure inside the tank is greater than the set pressure, the output signal of the controller should decrease, and at this point valve A should gradually close. When the output signal reaches the corresponding signal level for valve B, valve B should then gradually open

It’s similar to the principle of automatic backwashing; it mainly relies on pressure settings, with control valves that function as interlocks to regulate the on/off state of A and B

Yes, I might have put it in general terms; it’s the situation you mentioned.