Due to Economic Dispatch, it is critical for a power generation plant to achieve the lowest load possible. This limits financial exposure while keeping the unit on-line during short periods of low prices.

Program Topics

  • Market Conditions and Drivers
  • Low Load Operation Optimization
  • Plant Cycling
  • Short Term Shutdown and Startup

Power Generation Industry Drivers

Current Market Conditions

  • Cheap Natural Gas
  • Impact of Take or Pay Renewable Energy (Wind and Solar)
  • Environmental Regulations
  • Increasing O&M Costs
  • Low Load Growth

Economic Impact of Negative LMPs

500 MW Plant with Margin Operating Price of $15/MWH
LMP MW $$ Loss/Hr $$ Loss/Day
$0  500 $0 $0
($10) 500 ($5,000)  ($120,000) 
($25) 500 ($12,500)  ($300,000) 
($50) 500 ($25,000)   ($600,000) 
($100) 500 ($50,000) ($1,200,000) 
($200) 500 ($100,000)  ($2,400,000) 
50% Load
$0 250 $0 $0
($10) 250 ($2,500) ($60,000)
($25) 250 ($6,250) ($150,000)
($50) 250 ($12,500) ($300,000)
($100) 250 ($25,000) ($600,000)
($200) 250 ($50,000) ($120,000)
20% Load
0 100 $0 $0
 ($10) 100 ($1,000) ($24,000)
($25) 100 ($2,500) ($60,000)
($50) 100 ($5,000) ($120,000)
($100) 100 ($10,000) ($240,000)
($200) 100 ($20,000) ($480,000)

Case in Point

500 MW Plant, currently self-scheduled into market evaluated must-run versus economic dispatch

  • Evaluate:
    • Minimum Load
    • Unit Startup Costs
    • Unit Start Times
    • Ramp Rates
    • Emissions
    • Maintenance Impacts
  • How much cycling is acceptable and what are the long-term effects?

Factors to Improve Unit Marketability

  • Very low load capabilities
  • Increased ramp rate (10+ MW/min)
  • Reduced startup times (cold and hot)
  • Reduced startup costs
  • Reduced station service

Goals and Objectives

With this conceptually developed, studied, and refined program and a team with hands on experience at an existing power plant, achieve the lowest possible stable load with a concentration on low hanging fruit and no capital input.

Process

  • Identify and document Client’s low load objectives
  • Interview plant staff
    • Review low load history
    • Expose known potential obstacles
  • Collect data and drawings
    • Design and operating data
    • Operations procedures
    • Equipment drawings and manuals
  • Perform onsite unit testing with different mill combinations
  • Collaborative effort between engineering, operations, and EAPC team
  • Collect real time data and identify system limitations
  • Evaluate data, eliminate limitations, retest to lower load

Potential Boiler Issues

  • Ability to make steam temperature
  • Coal mill turndown
  • Burner low load stability
  • Dependence on igniters
  • Inadequate coal drying
  • Control dampers out-of-range
  • Low back-end temperature
  • Boiler tube failures
  • Cracking in dissimilar metal welds
  • Increased tendency for oxidation and corrosion

Boiler Tasks

  • Review scanners
  • Review igniters
  • Review coal mill low load operation pattern
  • Shorten time required for mill startup and mill shutdown
  • Boiler condition assessment

Potential Steam Turbine Issues

  • Minimum allowable amount of SH
  • Main steam–RH steam d/T
  • Minimum steam flow requirement (minimum exhaust vel)
  • Last stage erosion (moisture and droplet size)
  • Low load back pressure issue
  • Avoid use of exhaust hood sprays for extended periods (140F)
  • Steam seals

Potential Turbine/Generator Rotor Failure Issues

  • Turbine blade root locking shim migration
  • Generator rotor cracking

Potential AQCS Adaption Challenges

  • SCR temp (economizer and/or SCR bypass)
  • SNCR temp window tuning
  • Scrubber operation

Boiler Feedwater Pumps

  • Turbine driven pumps
    • Steam source transition load
    • Compare to sliding pressure control needs
  • Motor driven pumps
    • Low load pump curve versus FWR and recirculating valve

Auxiliary Steam System

  • Extraction steam uses (other than cycle)
    • Air preheating
    • Plant heating and cooling
  • Auxiliary steam availability
    • Turbine extraction
    • Multi-unit interconnection
    • Auxiliary boiler

Short-Term Unit Shutdown and Startup

  • Economic conditions, negative LMPs may require unit to be shutdown (from days to a week or longer)
  • Revise existing shutdown and startup procedures to bottle of the unit to preserve temperature and pressure and reduce startup times
  • Reduce or eliminate all unnecessary station service
  • Main issues for a quick startups (water chemistry issues and turbine metal mismatch temps)
  • Same potential negative impacts as unit cycling, but at a reduced rate

Unit Cycling

  • Clearly identify objectives. May include an engineering study
  • Assign three teams, identify potential failure mechanisms
    • Boiler team
    • Turbine-Generator team
    • BOP team
  • Negative impacts
    • Increased thermal stresses, chemical corrosion, loss of equipment life
    • Boiler water chemistry (new philosophy and controls)
    • Increased safety risk due to daily shutdowns and startups

Economic Conditions Drive the Power Generation Load Philosophy

  • Lower load optimization is achievable and makes the unit marketable and competitive
  • Short-term shutdowns and startups and a unit cycling program will follow a recommended engineering study