Understanding Centrifugal Air Compressor Capacity Controls 원심 공기 압축기 용량 제어 이해

https://www.airbestpractices.com/technology/air-compressors/understanding-centrifugal-air-compressor-capacity-controls

Understanding Centrifugal Air Compressor Capacity Controls

 

Compressed Air Best Practices® (CABP) Magazine recently caught up with Compressed Air and Gas Institute’s (CAGI).

CABP: Gentlemen, thanks for the series of articles on centrifugal compressors. Why have you selected centrifugal compressor capacity controls for this interview, and can you give a brief introduction?
CABP: 여러분, 원심 압축기에 대한 일련의 기사에 감사드립니다. 이 인터뷰에서 원심 압축기 용량 제어를 선택한 이유는 무엇이며, 간단히 소개해 주시겠습니까?

A centrifugal compressor's flow and pressure are typically controlled by a combination of an inlet control device and an unloading valve (UV).
원심 압축기의 흐름과 압력은 일반적으로 입구 제어 장치와 언로딩 밸브(UV)의 조합으로 제어됩니다.

압축기 입구 제어는 차압으로 제어하는 Inlet Throttle valve와 유량을 제어하는 Inlet Guide vane으로 나눌 수 있습니다.

Solutions for Inlet Regulation 입구 조절을 위한 솔루션

The inlet can be throttled on a dynamic compressor to continuously reduce the capacity of the compressor. The minimum flow is determined when the pressure ratio reaches the pump limit and the machine reaches maximum pressure. The regulation range, or turndown, is determined by the design of the machine. For example, turndown is affected by the number of stages and the impeller design. Regulation range is also affected by external factors, such as inlet air conditions (temperature, pressure, and humidity), and coolant temperature.
입구는 동적 압축기에서 조절되어 압축기의 용량을 지속적으로 줄일 수 있습니다. 최소 유량은 압력 비율이 펌프 한계에 도달하고 기계가 최대 압력에 도달할 때 결정됩니다. 조절 범위 또는 턴다운은 기계의 설계에 따라 결정됩니다. 예를 들어, 턴다운은 단계 수와 임펠러 설계의 영향을 받습니다. 조절 범위는 입구 공기 조건(온도, 압력 및 습도) 및 냉각수 온도와 같은 외부 요인의 영향을 받습니다.

입구 조절 범위는 온도, 압력, 습도, 쿨러로 들어가는 물온도 등과 같은 입구 조건들에 따라 변화할 수 있습니다.

 

 

입구 온도가 감소하면 유량은 증가합니다. 
입구 온도가 증가하면 유량은 감소합니다.

입도 온도 조건이 다양할 경우 압축기는 높은 온도에서 설계를 해야 합니다. 그래야 온도가 감소하더라도 유량이 증가하기 때문에 운전이 가능하나 낮은 온도에서 설계를 하게 될 경우 온도가 증가하면 유량이 감소하기 때문에 압축기 운전이 되지 않을 수 있습니다.

 

Inlet Control Devices 입구 제어 장치

The following are two methods for throttling the inlet: 흡입구를 조절하는 두 가지 방법은 다음과 같습니다.

Inlet butterfly valve (IBV): The inlet butterfly valve may be driven electronically or pneumatically, and as it closes it creates a pressure drop across the valve, effectively reducing the inlet pressure into the compressor and throttling the compressor's ability to make pressure and subsequently flow.
흡입 버터플라이 밸브(IBV): 흡입 버터플라이 밸브는 전자식 또는 공압식으로 구동되며, 닫히면 밸브 전체에 압력 강하가 발생하여 압축기로 들어가는 흡입 압력이 효과적으로 감소하고 압축기가 압력을 가하고 이어서 흐르는 능력이 조절됩니다.

 

 

입구압력이 낮아질 경우 유량도 줄어드는 경향

Inlet Guide Vanes or (IGVs): The inlet guide vanes may also be driven electronically or pneumatically, and are a series of radial blades arranged in the intake. These vanes, in the wide-open position, are parallel to the airflow, and at fully closed are at 90 degrees to airflow. As the guide vanes are rotated from full open to partially closed, they cause the drawn-in gas to rotate in the same direction as the impeller. The pre-swirl changes the incidence angle of the incoming air as it approaches the inducer section of the impeller, effectively reducing the energy required to produce pressure and flow. The use of IGVs can effectively throttle the compressor with the added benefit of being more efficient. Depending on where you are operating on the compressor curve, a user may see up to a 9 percent efficiency gain over standard IBV throttling.
입구 가이드 베인 또는 (IGV): 입구 가이드 베인은 전자 또는 공압으로 구동될 수 있으며, 흡기구에 배열된 일련의 방사형 블레이드입니다. 이러한 베인은 완전히 열린 위치에서 공기 흐름과 평행하고 완전히 닫힌 상태에서는 공기 흐름과 90도 각도를 이룹니다. 가이드 베인이 완전히 열린 상태에서 부분적으로 닫힌 상태로 회전하면 흡입된 가스가 임펠러와 같은 방향으로 회전합니다. 사전 소용돌이는 임펠러의 유도기 섹션에 접근함에 따라 유입 공기의 입사각을 변경하여 압력과 흐름을 생성하는 데 필요한 에너지를 효과적으로 줄입니다. IGV를 사용하면 압축기를 효과적으로 조절하고 효율성이 더 높아질 수 있습니다. 압축기 곡선에서 어느 위치에서 작동하느냐에 따라 사용자는 표준 IBV 조절보다 최대 9%의 효율성 이득을 볼 수 있습니다.

The load set point of a centrifugal compressor is typically at a given pressure, so when the system pressure falls below a given level, the compressor will load.
원심 압축기의 부하 설정점은 일반적으로 주어진 압력이므로 시스템 압력이 주어진 수준 아래로 떨어지면 압축기가 부하됩니다.

 

Control and Regulating System for Centrifugal Compressors
원심 압축기용 제어 및 조절 시스템

1. Auto-Dual Control (See Figure 1)

The standard regulation is achieved by means of an inlet butterfly valve (IBV), or inlet guide vanes (IGVs) and controller.
The compressor discharge pressure set point will be set at the desired level and the IBV or IGVs will modulate the compressor inlet to maintain constant discharge pressure over the control (B®C) range.
압축기 배출 압력 설정점은 원하는 수준으로 설정되고 IBV 또는 IGV는 압축기 입구를 조절하여 제어(B®C) 범위 내에서 일정한 배출 압력을 유지합니다.

At the minimum throttle point (C), the IBV or IGV valve stops closing, allowing the discharge pressure to rise to the unload set point. At this moment the compressor will unload, the IBV or IGV will close, and an unloading valve fully opens.
최소 스로틀 지점(C)에서 IBV 또는 IGV 밸브는 닫히지 않아 배출 압력이 언로드 설정 지점까지 상승합니다. 이 순간 압축기는 언로드되고 IBV 또는 IGV는 닫히고 언로딩 밸브가 완전히 열립니다.

The compressor remains in the unloaded condition until the compressor resumes load at full flow and the cycle is repeated. Reloading time varies in this control method, and depending on the system’s storage capacities relative to the demand swings, it may be advisable to install measures (additional compressed air storage) to protect the process and the compressor against short cycling.
압축기는 압축기가 전체 흐름에서 부하를 재개하고 사이클이 반복될 때까지 무부하 상태를 유지합니다. 재장전 시간은 이 제어 방법에서 다르며 수요 변동에 대한 시스템의 저장 용량에 따라 공정과 압축기를 짧은 사이클로부터 보호하기 위한 조치(추가 압축 공기 저장)를 설치하는 것이 좋습니다.

If the compressor does not need to reload within a fixed time period, the unit may be configured to power down and stop. The controller will automatically restart and load in response to the system pressure falling to the load set point (A).
압축기가 고정된 시간 내에 재로드할 필요가 없는 경우, 장치는 전원을 끄고 멈추도록 구성될 수 있습니다. 컨트롤러는 시스템 압력이 부하 설정 지점(A)으로 떨어지면 자동으로 재시작하고 로드합니다.

 

2. Constant Pressure Control with Modulating Unloading Regulation (UV) (See Figure 2)

압축기 배출 압력 설정점은 원하는 수준으로 설정되고, IBV 또는 IGV는 압축기 입구를 조절하여 제어(A®B) 범위 내에서 일정한 배출 압력을 유지합니다. 일부 제어는 최대 언로딩 밸브(UV) 위치를 프로그래밍할 수도 있습니다. 이를 통해 소유자는 언로딩 작업을 (B®C) 사이 지점으로 제한하여 수요가 낮은 기간 동안 비효율적인 작업을 최소화할 수 있습니다. 일정 압력 제어 시스템은 순 압력 변동을 최소로 유지하면서 공기 출력을 지속적으로 제어하도록 설계되었습니다. 일정 압력은 많은 응용 분야에서 중요합니다.

Impact of External Factors on Regulation

 

How Surge Occurs in Centrifugal Compressors

Surge is the phenomenon of aerodynamic instability that can occur in centrifugal compressors.
The pressure rise in centrifugal compressors is created by imparting high velocity (kinetic energy) to the flow path of air through the impeller. The later conversion of velocity to pressure (potential energy) occurs in the diffuser, and possibly in the volute, if the compressor is so equipped.
서지는 원심 압축기에서 발생할 수 있는 공기역학적 불안정 현상입니다. 원심 압축기의 압력 상승은 임펠러를 통한 공기의 흐름 경로에 높은 속도(운동 에너지)를 부여하여 생성됩니다. 나중에 속도를 압력(위치 에너지)으로 변환하는 것은 디퓨저에서 발생하고, 압축기에 그렇게 장착된 경우 볼류트에서 발생할 수 있습니다.

Due to this limitation, any single compression stage cannot increase the pressure head above a limit of about 2.5 ratios (depending on design).

If the centrifugal compressor experiences surge during compressor operation, it is considered to be running in an unstable condition. Manufacturers take into consideration surge events when designing their compressors, and thus the occurrence of a single or even multiple surges will not reduce the life or damage the compressor. A qualified technician should be called if repeated surging is occurring. Manufacturers all use surge anticipation control to ensure reliable operation. There are several different methods to accomplish surge control.
원심 압축기가 압축기 작동 중에 서지를 경험하는 경우 불안정한 상태에서 작동하는 것으로 간주됩니다. 제조업체는 압축기를 설계할 때 서지 이벤트를 고려하므로 단일 또는 여러 서지가 발생하더라도 압축기의 수명이 단축되거나 손상되지 않습니다. 반복적인 서지가 발생하는 경우 자격을 갖춘 기술자를 불러야 합니다. 제조업체는 모두 서지 예상 제어를 사용하여 안정적인 작동을 보장합니다. 서지 제어를 달성하는 데는 여러 가지 방법이 있습니다.

Surge Control and Protection

1. Motor current control:이 제어를 사용하면 모터가 최소 전류 설정 값에 도달하면 언로딩 밸브가 열리기 시작하여 압축기가 서지하는 것을 방지합니다. 이 방법은 간단하고 직관적이지만 압축기의 실제 턴다운 범위를 항상 최적화하지는 않습니다.

2. Surge anticipation control optimization: 서지 예상 제어를 최적화하기 위해 컨트롤러는 기존 주변 유입 조건에 대한 서지 라인의 실제 위치를 모니터링하고 압축기 흐름이 서지 지점에 도달하면 언로딩 밸브를 열어 압축기가 서지되는 것을 방지합니다. 이 제어는 턴다운을 최적화하고 압축기가 기존 주변 유입 조건에 따라 실제 턴다운에서 작동할 수 있도록 합니다.