Power Plant Boiler Water
Ammonia, hydrazine and phosphate dosing with sampling monitoring to prevent corrosion and scaling.
Challenges
Feedwater and boiler water chemistry in power plants and industrial boilers is maintained by dosing: ammonia or another alkalising agent in feedwater to raise pH and limit acidic corrosion, an oxygen scavenger where required, and phosphate or similar treatment in boiler water to prevent scaling. Dosing errors affect boiler safety directly: low pH and high dissolved oxygen accelerate corrosion, while too much or too little phosphate causes hideout and deposits.
Injection points are at high pressure, so pumps must overcome drum or feedline pressure while delivering small, continuous and stable flows. Adjusting stroke length by hand after lab results is slow, especially at night or during load changes.
Our Approach
Boiler dosing is normally split into feedwater dosing and boiler-water dosing:
1. Ammonia or alkalising agent: dosed in proportion to feedwater flow and trimmed by online feedwater pH or conductivity. For higher injection pressures we use mechanical or hydraulic diaphragm metering pumps whose rated pressure exceeds the maximum operating pressure with margin.
2. Oxygen scavenger: an online dissolved oxygen analyzer at the deaerator outlet or economiser inlet can pace the scavenger pump. Measurement is at trace levels, so sensor choice and a leak-tight sample system matter.
3. Boiler-water phosphate: high-pressure drums usually need plunger or hydraulic diaphragm pumps, adjusted from phosphate and pH results or online data.
4. Dosing skid: tanks, mixers, duty/standby pumps, relief valves, gauges and pulsation dampers with a local panel that can link to the DCS for remote start/stop and stroke adjustment.
5. Sampling: pH, conductivity and dissolved oxygen transmitters can be grouped on the steam-water sampling rack after cooling and pressure reduction for stable readings.
Chemistry targets should be set by the plant chemistry team according to boiler parameters and applicable codes; we select pumps, analyzers and skid configuration to meet them. Please provide boiler pressure class, feedwater flow, injection pressure, chemicals and concentrations, and details of the existing sampling system.
Practical notes: check valves and relief valves on high-pressure dosing lines need periodic testing. Tanks for volatile chemicals such as ammonia should be closed with breather valves. Air ingress into dissolved oxygen sample lines gives falsely high readings and misleads dosing.