To satisfy the requirements of national pollution control and haze reduction policies

large scale coalfired heating boilers can be put into service but the small scale ones should be shut down

and centralized heating or new large-scale gas boilers should be used. As a result

a large number of small scale chain coal-fired boilers for heating in northern cities are facing shutdown

phased out or coal-to-gas conversion. In this paper

the technical study is carried out on the basis of a 70 MW chain coal-fired boiler which is modified into a natural gas boiler. The technical scheme and modification effect are introduced in detail

and the environmental protection parameters and economics before and after the modification are compared. The results show that

from the technical level

"coal to gas" can realize stable operation of the boiler

and the boiler thermal efficiency can reach higher than 95%. From the environmental protection level

ultra-low emission can be achieved

the mass concentration of NO_x emission is able to be controlled below 30 mg/m~3. From the economic level

although the fuel cost increases

the costs of desulfurization

denitrification

dust removal and other environmentally-friendly consumables and equipment costs

factory power consumption

fuel transportation and labor costs are reduced.