Powdered Sorbent Injection for Mercury Control in Flue Gas
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Solution Overview
Problem
Current sorbent injection methods for mercury removal in coal-fired power plants face challenges such as high sorbent requirements, costly halogen additives, limited residence times, and contamination of fly ash, leading to increased operational and maintenance costs, as well as environmental concerns.
Innovation Solution
A system and method for post-combustion mercury control using powdered sorbents injected downstream of particulate removal systems, followed by wet flue gas desulfurization, where the sorbents are powdered activated carbon without halogens, and additives like organosulfides are injected to enhance mercury capture, allowing for longer residence times and improved separation from fly ash.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If halogen additives are used to improve mercury capture, then mercury removal efficiency is improved, but corrosion of duct system and equipment increases
Solution Approach 1:
The patent uses powdered activated carbon (PAC) as a disposable sorbent material that can be injected in large quantities to capture mercury without causing corrosion. The PAC is consumed in the process and replaced regularly, avoiding the long-term corrosion damage caused by halogen additives while maintaining effective mercury removal.
Solution Approach 2:
The patent introduces powdered activated carbon as an intermediary substance between the flue gas and the duct system. The PAC captures mercury through adsorption in a neutral chemical process, serving as a mediator that removes the harmful substance (mercury) without introducing corrosive effects to the equipment.
2Reliability
If bromine is used as halogen additive to improve mercury capture, then mercury removal efficiency is improved, but environmental harm increases
Solution Approach 1:
The patent employs disposable powdered activated carbon that can be safely disposed of after use. Unlike bromine which persists in the environment and causes ozone depletion, the PAC can be contained and disposed of as solid waste, eliminating the long-term environmental harm associated with halogen emissions.
Solution Approach 2:
The patent converts the potential harm of using chemical additives by selecting a material (PAC) that is inherently safe for the environment. The PAC's high surface area and adsorption capacity provide the benefit of mercury removal while its carbon-based composition ensures it does not create harmful environmental byproducts like ozone depletion or carcinogenic compounds.
3Reliability
If powdered sorbent is injected upstream of particulate removal system, then mercury capture is improved, but fly ash quality is degraded
Solution Approach 1:
The patent segments the mercury removal process from the fly ash collection process by injecting PAC downstream of the particulate removal system. This separation allows the fly ash to be collected with its original quality intact, while the PAC handles mercury capture in a separate stage, preventing contamination of the fly ash product.
Solution Approach 2:
Instead of the conventional approach of injecting sorbent upstream of particulate removal, the patent inverts the sequence by injecting PAC downstream. This reversal of the injection timing and location prevents the sorbent from mixing with fly ash, thereby maintaining fly ash quality while still achieving effective mercury capture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces mercury concentrations in both the air and water phases of the flue gas desulfurization system, decreases the need for halogen additives, and maintains the quality of fly ash for sale, resulting in cost savings and improved environmental outcomes.
Implementation Method 1
the powdered sorbent disperses and adsorbs mercury and other unwanted constituents in the flue gas
Implementation Method 2
A high percentage of mercury in the flue gas will partition to a wet flue gas desulfurization liquid when it is found in the oxidized form
Data Source
AI summary
A system for cleaning flue gas, the system including a particulate removal system; an additive injector positioned downstream of the particulate removal system, for injecting an additive into the flue gas; a powdered sorbent injector positioned downstream of the additive injector, for injecting powdered sorbents, wherein no powdered sorbent injectors are positioned upstream of the particulate removal system; and a flue gas desulfurization system positioned downstream from the powdered sorbent injector, wherein no other processing apparatus is located between the powdered sorbent injector and the flue gas desulfurization system.