Device and method for controlling chemical injection into boiler

Patent metadata

Field	Value
Publication number	US-10179743-B2
Application number	US-201515115463-A
Country	US
Kind code	B2
Filing date	Feb 23, 2015
Priority date	Feb 28, 2014
Publication date	Jan 15, 2019
Grant date	Jan 15, 2019

Abstract

A device for controlling injection of chemical into a boiler and a chemical injection method can control an injection amount such that a chemical concentration is obtained as per a target even in a boiler feed-water facility where a flow rate of feed-water varies to a large extent in a short period. The device controls an amount discharged by a chemical injection pump in proportion to a flow rate measured by a flowmeter. An average chemical concentration in a feed-water is calculated from an amount of feed-water per predetermined period obtained by the flowmeter and a reduction in the amount of chemical in a tank per predetermined period obtained by a sensor. The chemical injection pump is controlled on the basis of the calculated average chemical concentration and a preset target chemical concentration of the feed-water so that the average chemical concentration is within the target chemical concentration range.

First claim

The invention claimed is:

1. A device for controlling chemical injection into a boiler, the device comprising:
a feed-water line for supplying feed-water from a feed-water tank to a boiler through a feed-water pipe provided with a feed-water pump;
a feed-water flow rate measuring device for measuring a flow rate of the feed-water flowing through the feed-water pipe;
a chemical injection pump for injecting a chemical liquid containing one or more chemicals for boiler water treatment into the feed-water line, the chemical liquid being stored in a chemical tank;
a chemical liquid amount measuring device for measuring an amount of the chemical liquid stored in the chemical tank; and
a controller for controlling a discharge rate of the chemical injection pump in proportion to the flow rate measured by the feed-water flow rate measuring device,
wherein an average chemical concentration in the feed-water is calculated from a feed-water volume per a predetermined period and a reduction amount of the chemical liquid in the chemical tank per the predetermined period, the feed-water volume per the predetermined period being determined by the feed-water flow rate measuring device and the reduction amount of the chemical liquid in the chemical tank being determined by the chemical liquid amount measuring device,
the controller controls the chemical injection pump to operate at a target discharge rate, the target discharge rate being resulted from multiplying the flow rate measured by the feed-water flow rate measuring device by a proportionality coefficient, in accordance with a preset target chemical concentration in the feed-water and the calculated average chemical concentration such that the average chemical concentration is held within a target chemical concentration range,
the controller corrects the proportionality coefficient in accordance with a difference between the preset target chemical concentration in the feed-water and the calculated average chemical concentration,
when the average chemical concentration in the feed-water is lower than a lower limit value of the target chemical concentration range, the proportionality coefficient is corrected to increase by multiplying the proportionality coefficient by a correction coefficient that corresponds to a difference between the lower limit value and the average chemical concentration, and
when the average chemical concentration in the feed-water is higher than an upper limit value of the target chemical concentration range, the proportionality coefficient is corrected to decrease by multiplying the proportionality coefficient by a correction coefficient that corresponds to a difference between the higher limit value and the average chemical concentration.

2. A method for controlling chemical injection into a boiler, comprising:
supplying feed-water from a feed-water tank to a boiler through a feed-water pipe provided with a feed-water pump;
measuring a flow rate of the feed-water flowing through the feed-water pipe;
injecting a chemical liquid stored in a chemical tank into a feed-water line;
measuring an amount of the chemical liquid stored in the chemical tank;
calculating an average chemical concentration in the feed-water from a feed-water amount per predetermined period and a reduction amount of the chemical liquid in the chemical tank per the predetermined period, the feed-water amount per predetermined period being determined by a feed-water flow rate measuring device, the reduction amount of the chemical liquid in the chemical tank per the predetermined period being determined by a chemical liquid amount measuring device;
controlling a chemical injection pump to operate at a target discharge rate, the target discharge rate being resulted from multiplying the flow rate by a proportionality coefficient in accordance with a preset target chemical concentration in the feed-water and the calculated average chemical concentration such that the average chemical concentration is held within a target chemical concentration range; and
correcting the proportionality coefficient in accordance with a difference between the preset target chemical concentration in the feed-water and the average chemical concentration calculated,
wherein, when the average chemical concentration in the feed-water is lower than a lower limit value of the target chemical concentration range, the proportionality coefficient is corrected to increase by multiplying the proportionality coefficient by a correction coefficient that corresponds to a difference between the lower limit value and the average chemical concentration, and
when the average chemical concentration in the feed-water is higher than an upper limit value of the target chemical concentration range, the proportionality coefficient is corrected to decrease by multiplying the proportionality coefficient by a correction coefficient that corresponds to a difference between the higher limit value and the average chemical concentration.

Assignees

• Kurita Water Ind Ltd

Inventors

• Shimpo Chikako
• Shimura Yukimasa

Classifications

• C02F2209/006

  comprising a software program or a logic diagram · CPC title

• C02F1/686 Primary

  Devices for dosing liquid additives · CPC title

• F22B37/025

  Devices and methods for diminishing corrosion, e.g. by preventing cooling beneath the dew point · CPC title

• C02F2209/40

  Liquid flow rate · CPC title

• C02F2209/005

  Processes using a programmable logic controller [PLC] · CPC title