Oil Degumming System

Overview

Oil degumming is the first step in refining crude oil extracted from seeds. Crude oil contains 1.5–3.5% phospholipids (gums), complex molecules consisting of glycerol, fatty acids, phosphate groups, and sometimes metals (iron, copper). These gums cause rancidity, haze, and poor storage stability. Degumming removes them via acid hydration and centrifugal settling.

The process is mechanical, not chemical, no alkali or high temperatures. Citric or phosphoric acid is mixed with water and emulsified into the crude oil, converting non-hydrating phospholipids into hydrating forms that precipitate. A continuous Gum Separation Centrifuge then separates the gum solids from the clarified oil.

Hydration mechanism

Crude oil contains two types of phospholipids: those already hydrating (hydratable) and those non-hydrating. The non-hydrating form is held in suspension by mineral impurities. When small amounts of water, typically 1–2% of oil weight, are dispersed into the oil with emulsifying energy, both types swell as water enters their molecular structure. Simultaneously, citric acid (0.2–0.5% by mass) lowers pH, destabilizing the suspended state.

The Hydrator Mixer is a stainless jacketed tank with a high-shear Hydrator Agitator. The crude oil is admitted first, then heated to 45–60°C for optimal viscosity. The Acid Dosing System system injects a premixed solution of water and citric acid at controlled rate, typically 1–2 cc per kg oil per minute. The agitator shears this dose into fine droplets, dispersing them throughout the oil.

Residence time in the hydrator is 10–20 minutes. The oil then flows to the Temperature Conditioning Vessel, a hold vessel kept at constant temperature to allow gum particles to settle and aggregate.

Centrifugal separation

The Gum Separation Centrifuge is a continuous three-phase decanter centrifuge spinning at 1500–3000 rpm. Oil and water enter the bowl's center; as the rotor spins, they separate radially by density. The denser water and gum solids move outward; the lighter oil moves inward and overflows.

An internal Centrifuge Scroll, a slow conveyor, gradually moves settled gum solids toward the discharge port at the bowl's apex, while oil exits continuously from the center-line discharge.

Separation efficiency is typically 85–95%, leaving trace phospholipids (< 100 ppm) in the degummed oil. Complete removal would require washing, not typically done at this stage.

Cooling and discharge

The hot degummed oil (typically 50–60°C) flows through the Cooling Exchanger, a water-cooled heat exchanger that brings it to 35–40°C. This reduces oxidation risk during storage and improves handling for the next stage, either Oil Bleaching Vessel (for food oil) or bulk storage.

Gum solids exit from the centrifuge as a wet cake (30–40% water). This material is typically burned as fuel or sent to landfill; industrial users may recover it as a phospholipid concentrate for animal feed additives.

pH control

Optimal degumming occurs at pH 3.0–4.5 in the hydrator. A pH Sensor continuously monitors this; the Acid Dosing System pump adjusts rate to maintain setpoint. Underdosing leaves residual gum; overdosing wastes acid and risks leaving acidic oil (which must later be neutralized in refining).

Integration with refining

Degumming is always the first step in edible oil refining. Crude oil directly from Solvent Extractor or Oilseed Expeller Press contains mucilaginous matter that interferes with all downstream processes, bleaching, deodorizing, and eventual product stability.

The sequence is: crude oil → degumming → Oil Bleaching Vessel → Oil Deodorizer.

Industrial refineries often combine degumming with Oil Bleaching Vessel in a single unit (co-processing), but separate equipment allows independent optimization of each step.

Waste and sustainability

The gum stream (wet sediment) is typically 3–5% of original crude oil weight. Modern facilities treat this as a byproduct: heating for fuel recovery, or extraction of the phospholipid fraction for specialty products (lecithin). Untreated gum disposal must account for moisture content and storage stability.