catalyst, causing the reduction of NOx.
The technology is capable of reducing
NOx emissions to near zero.
specify an SCR that would deliver a
5 ppm NOx reduction with an incoming
NOx level of 50 ppm. Lower NOx could be
attained by merely adjusting the Compu-NOx to deliver lower NOx to the catalyst.
Selective catalytic reduction
technology is capable of reduc-
ing NOx emissions to near zero.
Del Monte knew that while today’s
limit may be 6 ppm, continued high pollution levels in the valley would most likely
result in the imposition of lower emission
limits for its boilers. Accommodating
for this scenario, the facility decided to
Generating Electricity for Less
The local utility had been raising
Del Monte’s electricity rate needed to
process fruit every year, with electricity
projected to exceed 12 cents/k Wh by
2010. Mortensen and his staff looked
to dampen the effect of these regular
rate increases, recognizing the electric-generating potential from using a back-pressure turbine to provide steam to
the 60 psig header feeding the fruit cup
line. A feasibility study was conducted
Figure 1. Back-Pressure Steam Turbine, Del Monte Foods’ Super Boiler.
Source: Benz Air Engineering
to find the optimum steam conditions
to specify for the new boiler, concluding
with 275 psig and 494 F and the back-pressure steam turbine generating electricity for less than 2 cents/kWh.
Del Monte hired TurboSteam of
Turners Falls, Mass., to provide a payback
analysis and a price quote for a turbine
generator with financing. TurboSteam
supplied a package design comprising a
single skid with one induction generator
that guaranteed 77 percent efficiency over
a 10-to- 1 turndown. The steam turbine
would be installed with a desuperheating
valve to maintain steam pressure in the
event of turbine trip or at extreme low-load conditions (fig. 1).
The operational data also served
to establish a baseline of steam system efficiency that would be compared to the efficiency resulting from
the upgrades. Rebates available from
California’s energy efficiency rebate
program would increase the return on
investment from the lower cost of operation resulting from efficiency.
Figure 2. Del Monte’s Super Boiler: Full-Load Boiler and Heat Recovery Process.
Incorporating Stack Gas
Only a small amount of condensate
from the steam to the new processing
lines could be recovered, the majority of
the 60 F makeup water being preheated
with process steam in the deaerator.
The process also required a substantial
amount of hot water, which was also
heated with process steam. Recognizing
these various sources represented a
substantial heat sink, Mortensen enlisted Benz Air Engineering Co. to design
and incorporate a heat recovery system
into the new boiler project.
A pinch analysis of preheating
boiler makeup and process water using
boiler flue gas heat recovery was used
to design a condensing heat exchanger.
The resulting design (fig. 2) integrated
the condensing heat exchanger into the
boiler system, which, when combined
with the control system, yielded some
novel features that would result in efficiency exceeding 93 percent:
l Installation of an additional heat
exchanger between the makeup
water and the feed water provided
significant reduction in the needed