Lime Dosing System

Industry:

Power Sector

Client:

Leading Power Player

Client requirement –

Conveying Hydrated Lime in free-flowing manner, without spillages and implementing a dust-free operation with metered dosing in a tank for neutralizing and thereafter for further FGD process.
To convey this hydrated lime powder without causing any risk of exposure to workers and work environment.
Fine Dosing Requirements:
- 01. Silo Loading Capacity: 2500 Kg/hr.
- 02. Controlled Discharge to prepare lime slurry: 154 Kg/hr.
- 03. With specific concentration of Lime vs. Water Slurry.

Why is lime dosing required?

Lime slurry been used in Flue-gas desulfurization (FGD) for controlling the acidic gases. In this process, sulphur dioxide (SO2) is removed from exhaust flue gases emanated from post combustion of fossil-fuel in thermal power plants.
The flue gases are introduced into an absorbing tower (Reactor tower) where the gases encounter a finely atomized alkaline (lime solution) slurry.
Consequently, acidic gases are absorbed by the slurry mixture and converted into solid salts which are removed by the particulate control device and bled out as per selected system.

The challenges

Ensuring less to no leakage of the material in the environment.
Assuring fine dosing as to maintain precise pH value of water in neutralizing tank.
Less maintenance issues and safely with easy operable.

Solution

We have proposed and installed mechanical conveying system for conveying Lime Powder.
The material is available in 2 batches of 25 kg & 50 kg bags.
We provided a feed hopper to unload the material manually. This will especially be useful to control the dust generation at the bag dumping area.
As there were space restriction along with low conveying capacity, we proposed bucket elevator. This will help in carrying out dust-free and weather tight operation.
From the feed hopper the material is dropped to the bucket elevator and lifted to destination storage silos.
As the material needs to be stored in two silos, we have diverted the flow of material using motorised flap type diverter valve. They are placed in conveying line because they are easy to operate and to maintain.
Material separation was done with utmost care so that the lime powder is completely settled down & separated from the air before leaving the system. This was achieved with separation units consisting of: Bin mounted bag filters.
As client required fine dosing, we have given rotary air lock for lime dosing application.
Thereafter, we have provided the VFD operated rotary air lock valve with max. inlet size & low volume to have blockage free operation.
Hence, using rotary air lock valve, we successfully achieved the desired fine dosing which was needed to maintain the accurate pH value in neutralizing tank for further FDG process.
Complete skid mounted neutralization system been supplied along with the dosing system.

Why mechanical conveying system?

Specific requirement for fine dosing of hydrated lime with complete dust-free operation with low power consumption as well as easy to operate.
Moreover, there were space restrictions & lower capacity. In such a situation, the hydrated lime dosing system – Bucket Elevator best suited the case as it reduces the material settling time (as no air involved in the process).

Value added by RIECO

The system installed was fully leak proof.
Rotary air lock valve arrangement provided in the system made sure the system required material flow rate is met.