Hogging & Holding
The “hogging and holding” system packages perform two distinct services: hogging and holding. During startup, or “hogging”, the vacuum system removes air from the condenser and any vacant space in the process. The system reduces the pressure in the process space to a pressure specified by the customer. During “holding”, the evacuation system removes a constant amount of air leakage by from the condenser. This allows the system to maintain a specified and desired pressure. This process is often referred to as “hogging and holding”.
Hogging and Holding in the Power and Cooking Industries
Power plants often use hogging and holding techniques in their process. The purpose of a vacuum in these applications is to minimize the back pressure on steam turbines. The vacuum pumps also remove non-condensables from the process stream. Air leakage into the process becomes more relevant because the condensers operate under vacuum in this process. The low pressure inside the condenser pulls more air through its leaks than at atmospheric pressure. This leakage is a common cause for process vapor contamination. Air leakage from piping, seals, and other equipment upstream of the condenser lower its heat transfer capabilities.
The process of evacuating and holding low pressure is found in vacuum cooking applications, as well. In these processes, vacuum pumps evacuate cooking vessels from atmospheric to a desired pressure. While cooking, the vessels must be held at a certain pressure. During this holding step, the vacuum system handles both the water vapor and the byproducts of cooking. Wintek’s engineers size vacuum systems to handle both cases.
In a steam power plant, a pre-condenser condenses water vapor from the steam turbine while under vacuum. Continuously removing air from the process stream preserves the condensing capacity of the condenser. Wintek designs systems using a hybrid jet liquid ring vacuum system or boosted liquid ring vacuum system for hogging and holding, depending on the particular application.